diff --git a/app/vlinsert/elasticsearch/elasticsearch.go b/app/vlinsert/elasticsearch/elasticsearch.go
index d511d37295..a7fb24823b 100644
--- a/app/vlinsert/elasticsearch/elasticsearch.go
+++ b/app/vlinsert/elasticsearch/elasticsearch.go
@@ -94,19 +94,20 @@ func RequestHandler(path string, w http.ResponseWriter, r *http.Request) bool {
 			httpserver.Errorf(w, r, "%s", err)
 			return true
 		}
+		if err := vlstorage.CanWriteData(); err != nil {
+			httpserver.Errorf(w, r, "%s", err)
+			return true
+		}
 		lr := logstorage.GetLogRows(cp.StreamFields, cp.IgnoreFields)
 		processLogMessage := cp.GetProcessLogMessageFunc(lr)
 		isGzip := r.Header.Get("Content-Encoding") == "gzip"
 		n, err := readBulkRequest(r.Body, isGzip, cp.TimeField, cp.MsgField, processLogMessage)
+		vlstorage.MustAddRows(lr)
+		logstorage.PutLogRows(lr)
 		if err != nil {
 			logger.Warnf("cannot decode log message #%d in /_bulk request: %s", n, err)
 			return true
 		}
-		err = vlstorage.AddRows(lr)
-		logstorage.PutLogRows(lr)
-		if err != nil {
-			httpserver.Errorf(w, r, "cannot insert rows: %s", err)
-		}
 
 		tookMs := time.Since(startTime).Milliseconds()
 		bw := bufferedwriter.Get(w)
@@ -132,7 +133,7 @@ var (
 )
 
 func readBulkRequest(r io.Reader, isGzip bool, timeField, msgField string,
-	processLogMessage func(timestamp int64, fields []logstorage.Field) error,
+	processLogMessage func(timestamp int64, fields []logstorage.Field),
 ) (int, error) {
 	// See https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-bulk.html
 
@@ -175,7 +176,7 @@ func readBulkRequest(r io.Reader, isGzip bool, timeField, msgField string,
 var lineBufferPool bytesutil.ByteBufferPool
 
 func readBulkLine(sc *bufio.Scanner, timeField, msgField string,
-	processLogMessage func(timestamp int64, fields []logstorage.Field) error,
+	processLogMessage func(timestamp int64, fields []logstorage.Field),
 ) (bool, error) {
 	var line []byte
 
@@ -222,11 +223,8 @@ func readBulkLine(sc *bufio.Scanner, timeField, msgField string,
 		ts = time.Now().UnixNano()
 	}
 	p.RenameField(msgField, "_msg")
-	err = processLogMessage(ts, p.Fields)
+	processLogMessage(ts, p.Fields)
 	logjson.PutParser(p)
-	if err != nil {
-		return false, err
-	}
 
 	return true, nil
 }
diff --git a/app/vlinsert/elasticsearch/elasticsearch_test.go b/app/vlinsert/elasticsearch/elasticsearch_test.go
index 3935e0dee6..09d1bf770c 100644
--- a/app/vlinsert/elasticsearch/elasticsearch_test.go
+++ b/app/vlinsert/elasticsearch/elasticsearch_test.go
@@ -15,9 +15,8 @@ func TestReadBulkRequestFailure(t *testing.T) {
 	f := func(data string) {
 		t.Helper()
 
-		processLogMessage := func(timestamp int64, fields []logstorage.Field) error {
+		processLogMessage := func(timestamp int64, fields []logstorage.Field) {
 			t.Fatalf("unexpected call to processLogMessage with timestamp=%d, fields=%s", timestamp, fields)
-			return nil
 		}
 
 		r := bytes.NewBufferString(data)
@@ -44,7 +43,7 @@ func TestReadBulkRequestSuccess(t *testing.T) {
 
 		var timestamps []int64
 		var result string
-		processLogMessage := func(timestamp int64, fields []logstorage.Field) error {
+		processLogMessage := func(timestamp int64, fields []logstorage.Field) {
 			timestamps = append(timestamps, timestamp)
 
 			a := make([]string, len(fields))
@@ -53,7 +52,6 @@ func TestReadBulkRequestSuccess(t *testing.T) {
 			}
 			s := "{" + strings.Join(a, ",") + "}\n"
 			result += s
-			return nil
 		}
 
 		// Read the request without compression
diff --git a/app/vlinsert/elasticsearch/elasticsearch_timing_test.go b/app/vlinsert/elasticsearch/elasticsearch_timing_test.go
index 5d8cca1b29..9a50fe0ebe 100644
--- a/app/vlinsert/elasticsearch/elasticsearch_timing_test.go
+++ b/app/vlinsert/elasticsearch/elasticsearch_timing_test.go
@@ -33,7 +33,7 @@ func benchmarkReadBulkRequest(b *testing.B, isGzip bool) {
 
 	timeField := "@timestamp"
 	msgField := "message"
-	processLogMessage := func(timestmap int64, fields []logstorage.Field) error { return nil }
+	processLogMessage := func(timestmap int64, fields []logstorage.Field) {}
 
 	b.ReportAllocs()
 	b.SetBytes(int64(len(data)))
diff --git a/app/vlinsert/insertutils/common_params.go b/app/vlinsert/insertutils/common_params.go
index 1852f22337..23f100775d 100644
--- a/app/vlinsert/insertutils/common_params.go
+++ b/app/vlinsert/insertutils/common_params.go
@@ -72,13 +72,13 @@ func GetCommonParams(r *http.Request) (*CommonParams, error) {
 }
 
 // GetProcessLogMessageFunc returns a function, which adds parsed log messages to lr.
-func (cp *CommonParams) GetProcessLogMessageFunc(lr *logstorage.LogRows) func(timestamp int64, fields []logstorage.Field) error {
-	return func(timestamp int64, fields []logstorage.Field) error {
+func (cp *CommonParams) GetProcessLogMessageFunc(lr *logstorage.LogRows) func(timestamp int64, fields []logstorage.Field) {
+	return func(timestamp int64, fields []logstorage.Field) {
 		if len(fields) > *MaxFieldsPerLine {
 			rf := logstorage.RowFormatter(fields)
 			logger.Warnf("dropping log line with %d fields; it exceeds -insert.maxFieldsPerLine=%d; %s", len(fields), *MaxFieldsPerLine, rf)
 			rowsDroppedTotalTooManyFields.Inc()
-			return nil
+			return
 		}
 
 		lr.MustAdd(cp.TenantID, timestamp, fields)
@@ -87,14 +87,12 @@ func (cp *CommonParams) GetProcessLogMessageFunc(lr *logstorage.LogRows) func(ti
 			lr.ResetKeepSettings()
 			logger.Infof("remoteAddr=%s; requestURI=%s; ignoring log entry because of `debug` query arg: %s", cp.DebugRemoteAddr, cp.DebugRequestURI, s)
 			rowsDroppedTotalDebug.Inc()
-			return nil
+			return
 		}
 		if lr.NeedFlush() {
-			err := vlstorage.AddRows(lr)
+			vlstorage.MustAddRows(lr)
 			lr.ResetKeepSettings()
-			return err
 		}
-		return nil
 	}
 }
 
diff --git a/app/vlinsert/jsonline/jsonline.go b/app/vlinsert/jsonline/jsonline.go
index 863cf20479..caa86ccbfb 100644
--- a/app/vlinsert/jsonline/jsonline.go
+++ b/app/vlinsert/jsonline/jsonline.go
@@ -36,6 +36,10 @@ func RequestHandler(w http.ResponseWriter, r *http.Request) bool {
 		httpserver.Errorf(w, r, "%s", err)
 		return true
 	}
+	if err := vlstorage.CanWriteData(); err != nil {
+		httpserver.Errorf(w, r, "%s", err)
+		return true
+	}
 	lr := logstorage.GetLogRows(cp.StreamFields, cp.IgnoreFields)
 	processLogMessage := cp.GetProcessLogMessageFunc(lr)
 
@@ -75,12 +79,8 @@ func RequestHandler(w http.ResponseWriter, r *http.Request) bool {
 		rowsIngestedTotal.Inc()
 	}
 
-	err = vlstorage.AddRows(lr)
+	vlstorage.MustAddRows(lr)
 	logstorage.PutLogRows(lr)
-	if err != nil {
-		httpserver.Errorf(w, r, "cannot insert rows: %s", err)
-		return true
-	}
 
 	// update jsonlineRequestDuration only for successfully parsed requests.
 	// There is no need in updating jsonlineRequestDuration for request errors,
@@ -90,7 +90,7 @@ func RequestHandler(w http.ResponseWriter, r *http.Request) bool {
 	return true
 }
 
-func readLine(sc *bufio.Scanner, timeField, msgField string, processLogMessage func(timestamp int64, fields []logstorage.Field) error) (bool, error) {
+func readLine(sc *bufio.Scanner, timeField, msgField string, processLogMessage func(timestamp int64, fields []logstorage.Field)) (bool, error) {
 	var line []byte
 	for len(line) == 0 {
 		if !sc.Scan() {
@@ -117,11 +117,8 @@ func readLine(sc *bufio.Scanner, timeField, msgField string, processLogMessage f
 		ts = time.Now().UnixNano()
 	}
 	p.RenameField(msgField, "_msg")
-	err = processLogMessage(ts, p.Fields)
+	processLogMessage(ts, p.Fields)
 	logjson.PutParser(p)
-	if err != nil {
-		return false, err
-	}
 
 	return true, nil
 }
diff --git a/app/vlinsert/jsonline/jsonline_test.go b/app/vlinsert/jsonline/jsonline_test.go
index f6da725c32..86a917491e 100644
--- a/app/vlinsert/jsonline/jsonline_test.go
+++ b/app/vlinsert/jsonline/jsonline_test.go
@@ -16,7 +16,7 @@ func TestReadBulkRequestSuccess(t *testing.T) {
 
 		var timestamps []int64
 		var result string
-		processLogMessage := func(timestamp int64, fields []logstorage.Field) error {
+		processLogMessage := func(timestamp int64, fields []logstorage.Field) {
 			timestamps = append(timestamps, timestamp)
 
 			a := make([]string, len(fields))
@@ -25,8 +25,6 @@ func TestReadBulkRequestSuccess(t *testing.T) {
 			}
 			s := "{" + strings.Join(a, ",") + "}\n"
 			result += s
-
-			return nil
 		}
 
 		// Read the request without compression
diff --git a/app/vlinsert/loki/loki_json.go b/app/vlinsert/loki/loki_json.go
index 914b664129..263b1781ff 100644
--- a/app/vlinsert/loki/loki_json.go
+++ b/app/vlinsert/loki/loki_json.go
@@ -47,21 +47,20 @@ func handleJSON(r *http.Request, w http.ResponseWriter) bool {
 		httpserver.Errorf(w, r, "cannot parse common params from request: %s", err)
 		return true
 	}
+	if err := vlstorage.CanWriteData(); err != nil {
+		httpserver.Errorf(w, r, "%s", err)
+		return true
+	}
 	lr := logstorage.GetLogRows(cp.StreamFields, cp.IgnoreFields)
 	processLogMessage := cp.GetProcessLogMessageFunc(lr)
 	n, err := parseJSONRequest(data, processLogMessage)
+	vlstorage.MustAddRows(lr)
+	logstorage.PutLogRows(lr)
 	if err != nil {
-		logstorage.PutLogRows(lr)
-		httpserver.Errorf(w, r, "cannot parse Loki request: %s", err)
+		httpserver.Errorf(w, r, "cannot parse Loki json request: %s", err)
 		return true
 	}
 
-	err = vlstorage.AddRows(lr)
-	logstorage.PutLogRows(lr)
-	if err != nil {
-		httpserver.Errorf(w, r, "cannot insert rows: %s", err)
-		return true
-	}
 	rowsIngestedJSONTotal.Add(n)
 
 	// update lokiRequestJSONDuration only for successfully parsed requests
@@ -78,7 +77,7 @@ var (
 	lokiRequestJSONDuration = metrics.NewHistogram(`vl_http_request_duration_seconds{path="/insert/loki/api/v1/push",format="json"}`)
 )
 
-func parseJSONRequest(data []byte, processLogMessage func(timestamp int64, fields []logstorage.Field) error) (int, error) {
+func parseJSONRequest(data []byte, processLogMessage func(timestamp int64, fields []logstorage.Field)) (int, error) {
 	p := parserPool.Get()
 	defer parserPool.Put(p)
 	v, err := p.ParseBytes(data)
@@ -171,11 +170,7 @@ func parseJSONRequest(data []byte, processLogMessage func(timestamp int64, field
 				Name:  "_msg",
 				Value: bytesutil.ToUnsafeString(msg),
 			})
-			err = processLogMessage(ts, fields)
-			if err != nil {
-				return rowsIngested, err
-			}
-
+			processLogMessage(ts, fields)
 		}
 		rowsIngested += len(lines)
 	}
diff --git a/app/vlinsert/loki/loki_json_test.go b/app/vlinsert/loki/loki_json_test.go
index f285dd1f7c..93cf8652ad 100644
--- a/app/vlinsert/loki/loki_json_test.go
+++ b/app/vlinsert/loki/loki_json_test.go
@@ -11,9 +11,8 @@ import (
 func TestParseJSONRequestFailure(t *testing.T) {
 	f := func(s string) {
 		t.Helper()
-		n, err := parseJSONRequest([]byte(s), func(timestamp int64, fields []logstorage.Field) error {
+		n, err := parseJSONRequest([]byte(s), func(timestamp int64, fields []logstorage.Field) {
 			t.Fatalf("unexpected call to parseJSONRequest callback!")
-			return nil
 		})
 		if err == nil {
 			t.Fatalf("expecting non-nil error")
@@ -61,14 +60,13 @@ func TestParseJSONRequestSuccess(t *testing.T) {
 	f := func(s string, resultExpected string) {
 		t.Helper()
 		var lines []string
-		n, err := parseJSONRequest([]byte(s), func(timestamp int64, fields []logstorage.Field) error {
+		n, err := parseJSONRequest([]byte(s), func(timestamp int64, fields []logstorage.Field) {
 			var a []string
 			for _, f := range fields {
 				a = append(a, f.String())
 			}
 			line := fmt.Sprintf("_time:%d %s", timestamp, strings.Join(a, " "))
 			lines = append(lines, line)
-			return nil
 		})
 		if err != nil {
 			t.Fatalf("unexpected error: %s", err)
diff --git a/app/vlinsert/loki/loki_json_timing_test.go b/app/vlinsert/loki/loki_json_timing_test.go
index 37d922fc02..9c51f593a1 100644
--- a/app/vlinsert/loki/loki_json_timing_test.go
+++ b/app/vlinsert/loki/loki_json_timing_test.go
@@ -27,7 +27,7 @@ func benchmarkParseJSONRequest(b *testing.B, streams, rows, labels int) {
 	b.RunParallel(func(pb *testing.PB) {
 		data := getJSONBody(streams, rows, labels)
 		for pb.Next() {
-			_, err := parseJSONRequest(data, func(timestamp int64, fields []logstorage.Field) error { return nil })
+			_, err := parseJSONRequest(data, func(timestamp int64, fields []logstorage.Field) {})
 			if err != nil {
 				panic(fmt.Errorf("unexpected error: %s", err))
 			}
diff --git a/app/vlinsert/loki/loki_protobuf.go b/app/vlinsert/loki/loki_protobuf.go
index eb262dcc80..af489329b9 100644
--- a/app/vlinsert/loki/loki_protobuf.go
+++ b/app/vlinsert/loki/loki_protobuf.go
@@ -39,19 +39,17 @@ func handleProtobuf(r *http.Request, w http.ResponseWriter) bool {
 		httpserver.Errorf(w, r, "cannot parse common params from request: %s", err)
 		return true
 	}
+	if err := vlstorage.CanWriteData(); err != nil {
+		httpserver.Errorf(w, r, "%s", err)
+		return true
+	}
 	lr := logstorage.GetLogRows(cp.StreamFields, cp.IgnoreFields)
 	processLogMessage := cp.GetProcessLogMessageFunc(lr)
 	n, err := parseProtobufRequest(data, processLogMessage)
-	if err != nil {
-		logstorage.PutLogRows(lr)
-		httpserver.Errorf(w, r, "cannot parse Loki request: %s", err)
-		return true
-	}
-
-	err = vlstorage.AddRows(lr)
+	vlstorage.MustAddRows(lr)
 	logstorage.PutLogRows(lr)
 	if err != nil {
-		httpserver.Errorf(w, r, "cannot insert rows: %s", err)
+		httpserver.Errorf(w, r, "cannot parse Loki protobuf request: %s", err)
 		return true
 	}
 
@@ -71,7 +69,7 @@ var (
 	lokiRequestProtobufDuration = metrics.NewHistogram(`vl_http_request_duration_seconds{path="/insert/loki/api/v1/push",format="protobuf"}`)
 )
 
-func parseProtobufRequest(data []byte, processLogMessage func(timestamp int64, fields []logstorage.Field) error) (int, error) {
+func parseProtobufRequest(data []byte, processLogMessage func(timestamp int64, fields []logstorage.Field)) (int, error) {
 	bb := bytesBufPool.Get()
 	defer bytesBufPool.Put(bb)
 
@@ -114,10 +112,7 @@ func parseProtobufRequest(data []byte, processLogMessage func(timestamp int64, f
 			if ts == 0 {
 				ts = currentTimestamp
 			}
-			err = processLogMessage(ts, fields)
-			if err != nil {
-				return rowsIngested, err
-			}
+			processLogMessage(ts, fields)
 		}
 		rowsIngested += len(stream.Entries)
 	}
diff --git a/app/vlinsert/loki/loki_protobuf_test.go b/app/vlinsert/loki/loki_protobuf_test.go
index cc259bce58..f6eb5f0ec2 100644
--- a/app/vlinsert/loki/loki_protobuf_test.go
+++ b/app/vlinsert/loki/loki_protobuf_test.go
@@ -14,7 +14,7 @@ func TestParseProtobufRequestSuccess(t *testing.T) {
 	f := func(s string, resultExpected string) {
 		t.Helper()
 		var pr PushRequest
-		n, err := parseJSONRequest([]byte(s), func(timestamp int64, fields []logstorage.Field) error {
+		n, err := parseJSONRequest([]byte(s), func(timestamp int64, fields []logstorage.Field) {
 			msg := ""
 			for _, f := range fields {
 				if f.Name == "_msg" {
@@ -39,7 +39,6 @@ func TestParseProtobufRequestSuccess(t *testing.T) {
 					},
 				},
 			})
-			return nil
 		})
 		if err != nil {
 			t.Fatalf("unexpected error: %s", err)
@@ -55,14 +54,13 @@ func TestParseProtobufRequestSuccess(t *testing.T) {
 		encodedData := snappy.Encode(nil, data)
 
 		var lines []string
-		n, err = parseProtobufRequest(encodedData, func(timestamp int64, fields []logstorage.Field) error {
+		n, err = parseProtobufRequest(encodedData, func(timestamp int64, fields []logstorage.Field) {
 			var a []string
 			for _, f := range fields {
 				a = append(a, f.String())
 			}
 			line := fmt.Sprintf("_time:%d %s", timestamp, strings.Join(a, " "))
 			lines = append(lines, line)
-			return nil
 		})
 		if err != nil {
 			t.Fatalf("unexpected error: %s", err)
diff --git a/app/vlinsert/loki/loki_protobuf_timing_test.go b/app/vlinsert/loki/loki_protobuf_timing_test.go
index 230ab7a472..1b7cbd6476 100644
--- a/app/vlinsert/loki/loki_protobuf_timing_test.go
+++ b/app/vlinsert/loki/loki_protobuf_timing_test.go
@@ -29,7 +29,7 @@ func benchmarkParseProtobufRequest(b *testing.B, streams, rows, labels int) {
 	b.RunParallel(func(pb *testing.PB) {
 		body := getProtobufBody(streams, rows, labels)
 		for pb.Next() {
-			_, err := parseProtobufRequest(body, func(timestamp int64, fields []logstorage.Field) error { return nil })
+			_, err := parseProtobufRequest(body, func(timestamp int64, fields []logstorage.Field) {})
 			if err != nil {
 				panic(fmt.Errorf("unexpected error: %s", err))
 			}
diff --git a/app/vlstorage/main.go b/app/vlstorage/main.go
index 4533e7b25b..b1b55675c9 100644
--- a/app/vlstorage/main.go
+++ b/app/vlstorage/main.go
@@ -3,6 +3,7 @@ package vlstorage
 import (
 	"flag"
 	"fmt"
+	"net/http"
 	"sync"
 	"time"
 
@@ -10,6 +11,7 @@ import (
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/flagutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fs"
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/httpserver"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logstorage"
 )
@@ -30,7 +32,8 @@ var (
 		"see https://docs.victoriametrics.com/VictoriaLogs/keyConcepts.html#stream-fields ; see also -logIngestedRows")
 	logIngestedRows = flag.Bool("logIngestedRows", false, "Whether to log all the ingested log entries; this can be useful for debugging of data ingestion; "+
 		"see https://docs.victoriametrics.com/VictoriaLogs/data-ingestion/ ; see also -logNewStreams")
-	minFreeDiskSpaceBytes = flagutil.NewBytes("storage.minFreeDiskSpaceBytes", 10e6, "The minimum free disk space at -storageDataPath after which the storage stops accepting new data")
+	minFreeDiskSpaceBytes = flagutil.NewBytes("storage.minFreeDiskSpaceBytes", 10e6, "The minimum free disk space at -storageDataPath after which "+
+		"the storage stops accepting new data")
 )
 
 // Init initializes vlstorage.
@@ -77,9 +80,23 @@ func Stop() {
 var strg *logstorage.Storage
 var storageMetrics *metrics.Set
 
-// AddRows adds lr to vlstorage
-func AddRows(lr *logstorage.LogRows) error {
-	return strg.AddRows(lr)
+// CanWriteData returns non-nil error if it cannot write data to vlstorage.
+func CanWriteData() error {
+	if strg.IsReadOnly() {
+		return &httpserver.ErrorWithStatusCode{
+			Err: fmt.Errorf("cannot add rows into storage in read-only mode; the storage can be in read-only mode "+
+				"because of lack of free disk space at -storageDataPath=%s", *storageDataPath),
+			StatusCode: http.StatusTooManyRequests,
+		}
+	}
+	return nil
+}
+
+// MustAddRows adds lr to vlstorage
+//
+// It is advised to call CanWriteData() before calling MustAddRows()
+func MustAddRows(lr *logstorage.LogRows) {
+	strg.MustAddRows(lr)
 }
 
 // RunQuery runs the given q and calls processBlock for the returned data blocks
@@ -114,7 +131,6 @@ func initStorageMetrics(strg *logstorage.Storage) *metrics.Set {
 		if m().IsReadOnly {
 			return 1
 		}
-
 		return 0
 	})
 
diff --git a/lib/logstorage/datadb.go b/lib/logstorage/datadb.go
index a3fe6423d0..d5b42b62ee 100644
--- a/lib/logstorage/datadb.go
+++ b/lib/logstorage/datadb.go
@@ -2,8 +2,8 @@ package logstorage
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
+	"math"
 	"os"
 	"path/filepath"
 	"sort"
@@ -70,18 +70,15 @@ type datadb struct {
 	// stopCh is used for notifying background workers to stop
 	stopCh chan struct{}
 
-	// inmemoryPartsFlushersCount is the number of currently running in-memory parts flushers
+	// oldInmemoryPartsFlushersCount is the number of currently running flushers for old in-memory parts
 	//
 	// This variable must be accessed under partsLock.
-	inmemoryPartsFlushersCount int
+	oldInmemoryPartsFlushersCount int
 
 	// mergeWorkersCount is the number of currently running merge workers
 	//
 	// This variable must be accessed under partsLock.
 	mergeWorkersCount int
-
-	// isReadOnly indicates whether the storage is in read-only mode.
-	isReadOnly *uint32
 }
 
 // partWrapper is a wrapper for opened part.
@@ -141,7 +138,7 @@ func mustCreateDatadb(path string) {
 }
 
 // mustOpenDatadb opens datadb at the given path with the given flushInterval for in-memory data.
-func mustOpenDatadb(pt *partition, path string, flushInterval time.Duration, isReadOnly *uint32) *datadb {
+func mustOpenDatadb(pt *partition, path string, flushInterval time.Duration) *datadb {
 	// Remove temporary directories, which may be left after unclean shutdown.
 	fs.MustRemoveTemporaryDirs(path)
 
@@ -173,7 +170,6 @@ func mustOpenDatadb(pt *partition, path string, flushInterval time.Duration, isR
 		path:          path,
 		fileParts:     pws,
 		stopCh:        make(chan struct{}),
-		isReadOnly:    isReadOnly,
 	}
 
 	// Start merge workers in the hope they'll merge the remaining parts
@@ -187,51 +183,65 @@ func mustOpenDatadb(pt *partition, path string, flushInterval time.Duration, isR
 	return ddb
 }
 
-// startInmemoryPartsFlusherLocked starts flusher for in-memory parts to disk.
+// startOldInmemoryPartsFlusherLocked starts flusher for old in-memory parts to disk.
 //
 // This function must be called under partsLock.
-func (ddb *datadb) startInmemoryPartsFlusherLocked() {
+func (ddb *datadb) startOldInmemoryPartsFlusherLocked() {
 	maxWorkers := getMergeWorkersCount()
-	if ddb.inmemoryPartsFlushersCount >= maxWorkers {
+	if ddb.oldInmemoryPartsFlushersCount >= maxWorkers {
 		return
 	}
-	ddb.inmemoryPartsFlushersCount++
+	ddb.oldInmemoryPartsFlushersCount++
 	ddb.wg.Add(1)
 	go func() {
-		ddb.flushInmemoryParts()
+		ddb.flushOldInmemoryParts()
 		ddb.wg.Done()
 	}()
 }
 
-func (ddb *datadb) flushInmemoryParts() {
+func (ddb *datadb) flushOldInmemoryParts() {
 	ticker := time.NewTicker(time.Second)
 	defer ticker.Stop()
-	for {
+	var parts, partsToMerge []*partWrapper
+
+	for !needStop(ddb.stopCh) {
 		ddb.partsLock.Lock()
-		pws := make([]*partWrapper, 0, len(ddb.inmemoryParts))
-		pws = appendNotInMergePartsLocked(pws, ddb.inmemoryParts)
+		parts = appendNotInMergePartsLocked(parts[:0], ddb.inmemoryParts)
 		currentTime := time.Now()
-		partsToFlush := pws[:0]
-		for _, pw := range pws {
+		partsToFlush := parts[:0]
+		for _, pw := range parts {
 			if pw.flushDeadline.Before(currentTime) {
 				partsToFlush = append(partsToFlush, pw)
 			}
 		}
-		setInMergeLocked(partsToFlush)
-		if len(pws) == 0 {
-			ddb.inmemoryPartsFlushersCount--
+		// Do not take into account available disk space when flushing in-memory parts to disk,
+		// since otherwise the outdated in-memory parts may remain in-memory, which, in turn,
+		// may result in increased memory usage plus possible loss of historical data.
+		// It is better to crash on out of disk error in this case.
+		partsToMerge = appendPartsToMerge(partsToMerge[:0], partsToFlush, math.MaxUint64)
+		if len(partsToMerge) == 0 {
+			partsToMerge = append(partsToMerge[:0], partsToFlush...)
+		}
+		setInMergeLocked(partsToMerge)
+		needStop := false
+		if len(ddb.inmemoryParts) == 0 {
+			// There are no in-memory parts, so stop the flusher.
+			needStop = true
+			ddb.oldInmemoryPartsFlushersCount--
 		}
 		ddb.partsLock.Unlock()
 
-		if len(pws) == 0 {
-			// There are no in-memory parts, so stop the flusher.
+		if needStop {
 			return
 		}
-		err := ddb.mergePartsFinal(partsToFlush)
-		if err != nil {
-			logger.Panicf("FATAL: cannot flush inmemory parts to disk: %s", err)
+
+		ddb.mustMergeParts(partsToMerge, true)
+		if len(partsToMerge) < len(partsToFlush) {
+			// Continue merging remaining old in-memory parts from partsToFlush list.
+			continue
 		}
 
+		// There are no old in-memory parts to flush. Sleep for a while until these parts appear.
 		select {
 		case <-ddb.stopCh:
 			return
@@ -244,9 +254,6 @@ func (ddb *datadb) flushInmemoryParts() {
 //
 // This function must be called under locked partsLock.
 func (ddb *datadb) startMergeWorkerLocked() {
-	if ddb.IsReadOnly() {
-		return
-	}
 	maxWorkers := getMergeWorkersCount()
 	if ddb.mergeWorkersCount >= maxWorkers {
 		return
@@ -255,11 +262,8 @@ func (ddb *datadb) startMergeWorkerLocked() {
 	ddb.wg.Add(1)
 	go func() {
 		globalMergeLimitCh <- struct{}{}
-		err := ddb.mergeExistingParts()
+		ddb.mustMergeExistingParts()
 		<-globalMergeLimitCh
-		if err != nil && !errors.Is(err, errReadOnly) {
-			logger.Panicf("FATAL: background merge failed: %s", err)
-		}
 		ddb.wg.Done()
 	}()
 }
@@ -279,9 +283,9 @@ func getMergeWorkersCount() int {
 	return n
 }
 
-func (ddb *datadb) mergeExistingParts() error {
+func (ddb *datadb) mustMergeExistingParts() {
 	for !needStop(ddb.stopCh) {
-		maxOutBytes := ddb.availableDiskSpace()
+		maxOutBytes := availableDiskSpace(ddb.path)
 
 		ddb.partsLock.Lock()
 		parts := make([]*partWrapper, 0, len(ddb.inmemoryParts)+len(ddb.fileParts))
@@ -296,25 +300,11 @@ func (ddb *datadb) mergeExistingParts() error {
 
 		if len(pws) == 0 {
 			// Nothing to merge at the moment.
-			return nil
+			return
 		}
 
-		partsSize := getCompressedSize(pws)
-		if !ddb.reserveDiskSpace(partsSize) {
-			// There is no free disk space for the merge,
-			// because concurrent merge workers already reserved the disk space.
-			// Try again with smaller maxOutBytes.
-			ddb.releasePartsToMerge(pws)
-			continue
-		}
-		err := ddb.mergeParts(pws, false)
-		ddb.releaseDiskSpace(partsSize)
-		if err != nil {
-			return err
-		}
+		ddb.mustMergeParts(pws, false)
 	}
-
-	return nil
 }
 
 // appendNotInMergePartsLocked appends src parts with isInMerge=false to dst and returns the result.
@@ -349,29 +339,42 @@ func assertIsInMerge(pws []*partWrapper) {
 	}
 }
 
-var errReadOnly = errors.New("the storage is in read-only mode")
-
-// mergeParts merges pws to a single resulting part.
+// mustMergeParts merges pws to a single resulting part.
 //
-// if isFinal is set, then the resulting part will be saved to disk.
+// if isFinal is set, then the resulting part is guaranteed to be saved to disk.
+// The pws may remain unmerged after returning from the function if there is no enough disk space.
 //
 // All the parts inside pws must have isInMerge field set to true.
 // The isInMerge field inside pws parts is set to false before returning from the function.
-func (ddb *datadb) mergeParts(pws []*partWrapper, isFinal bool) error {
+func (ddb *datadb) mustMergeParts(pws []*partWrapper, isFinal bool) {
 	if len(pws) == 0 {
 		// Nothing to merge.
-		return nil
+		return
 	}
 
-	if ddb.IsReadOnly() {
-		return errReadOnly
-	}
 	assertIsInMerge(pws)
 	defer ddb.releasePartsToMerge(pws)
 
 	startTime := time.Now()
 
 	dstPartType := ddb.getDstPartType(pws, isFinal)
+	if dstPartType == partFile {
+		// Make sure there is enough disk space for performing the merge
+		partsSize := getCompressedSize(pws)
+		needReleaseDiskSpace := tryReserveDiskSpace(ddb.path, partsSize)
+		if needReleaseDiskSpace {
+			defer releaseDiskSpace(partsSize)
+		} else {
+			if !isFinal {
+				// There is no enough disk space for performing the non-final merge.
+				return
+			}
+			// Try performing final merge even if there is no enough disk space
+			// in order to persist in-memory data to disk.
+			// It is better to crash on out of memory error in this case.
+		}
+	}
+
 	if dstPartType == partInmemory {
 		atomic.AddUint64(&ddb.inmemoryMergesTotal, 1)
 		atomic.AddUint64(&ddb.inmemoryActiveMerges, 1)
@@ -392,7 +395,7 @@ func (ddb *datadb) mergeParts(pws []*partWrapper, isFinal bool) error {
 		mp.MustStoreToDisk(dstPartPath)
 		pwNew := ddb.openCreatedPart(&mp.ph, pws, nil, dstPartPath)
 		ddb.swapSrcWithDstParts(pws, pwNew, dstPartType)
-		return nil
+		return
 	}
 
 	// Prepare blockStreamReaders for source parts.
@@ -443,7 +446,7 @@ func (ddb *datadb) mergeParts(pws []*partWrapper, isFinal bool) error {
 		if dstPartType == partFile {
 			fs.MustRemoveAll(dstPartPath)
 		}
-		return nil
+		return
 	}
 
 	// Atomically swap the source parts with the newly created part.
@@ -463,7 +466,7 @@ func (ddb *datadb) mergeParts(pws []*partWrapper, isFinal bool) error {
 
 	d := time.Since(startTime)
 	if d <= 30*time.Second {
-		return nil
+		return
 	}
 
 	// Log stats for long merges.
@@ -471,7 +474,6 @@ func (ddb *datadb) mergeParts(pws []*partWrapper, isFinal bool) error {
 	rowsPerSec := int(float64(srcRowsCount) / durationSecs)
 	logger.Infof("merged (%d parts, %d rows, %d blocks, %d bytes) into (1 part, %d rows, %d blocks, %d bytes) in %.3f seconds at %d rows/sec to %q",
 		len(pws), srcRowsCount, srcBlocksCount, srcSize, dstRowsCount, dstBlocksCount, dstSize, durationSecs, rowsPerSec, dstPartPath)
-	return nil
 }
 
 func (ddb *datadb) nextMergeIdx() uint64 {
@@ -546,7 +548,7 @@ func (ddb *datadb) mustAddRows(lr *LogRows) {
 
 	ddb.partsLock.Lock()
 	ddb.inmemoryParts = append(ddb.inmemoryParts, pw)
-	ddb.startInmemoryPartsFlusherLocked()
+	ddb.startOldInmemoryPartsFlusherLocked()
 	if len(ddb.inmemoryParts) > defaultPartsToMerge {
 		ddb.startMergeWorkerLocked()
 	}
@@ -559,9 +561,6 @@ func (ddb *datadb) mustAddRows(lr *LogRows) {
 }
 
 func (ddb *datadb) needAssistedMergeForInmemoryPartsLocked() bool {
-	if ddb.IsReadOnly() {
-		return false
-	}
 	if len(ddb.inmemoryParts) < maxInmemoryPartsPerPartition {
 		return false
 	}
@@ -578,15 +577,16 @@ func (ddb *datadb) assistedMergeForInmemoryParts() {
 	ddb.partsLock.Lock()
 	parts := make([]*partWrapper, 0, len(ddb.inmemoryParts))
 	parts = appendNotInMergePartsLocked(parts, ddb.inmemoryParts)
-	pws := appendPartsToMerge(nil, parts, (1<<64)-1)
+	// Do not take into account available disk space when merging in-memory parts,
+	// since otherwise the outdated in-memory parts may remain in-memory, which, in turn,
+	// may result in increased memory usage plus possible loss of historical data.
+	// It is better to crash on out of disk error in this case.
+	pws := make([]*partWrapper, 0, len(parts))
+	pws = appendPartsToMerge(pws[:0], parts, math.MaxUint64)
 	setInMergeLocked(pws)
 	ddb.partsLock.Unlock()
 
-	err := ddb.mergeParts(pws, false)
-	if err == nil || errors.Is(err, errReadOnly) {
-		return
-	}
-	logger.Panicf("FATAL: cannot perform assisted merge for in-memory parts: %s", err)
+	ddb.mustMergeParts(pws, false)
 }
 
 // DatadbStats contains various stats for datadb.
@@ -675,12 +675,18 @@ func (ddb *datadb) debugFlush() {
 	// Nothing to do, since all the ingested data is available for search via ddb.inmemoryParts.
 }
 
-func (ddb *datadb) mergePartsFinal(pws []*partWrapper) error {
-	assertIsInMerge(pws)
+func (ddb *datadb) mustFlushInmemoryPartsToDisk() {
+	ddb.partsLock.Lock()
+	pws := append([]*partWrapper{}, ddb.inmemoryParts...)
+	setInMergeLocked(pws)
+	ddb.partsLock.Unlock()
 
 	var pwsChunk []*partWrapper
 	for len(pws) > 0 {
-		pwsChunk = appendPartsToMerge(pwsChunk[:0], pws, (1<<64)-1)
+		// Do not take into account available disk space when performing the final flush of in-memory parts to disk,
+		// since otherwise these parts will be lost.
+		// It is better to crash on out of disk error in this case.
+		pwsChunk = appendPartsToMerge(pwsChunk[:0], pws, math.MaxUint64)
 		if len(pwsChunk) == 0 {
 			pwsChunk = append(pwsChunk[:0], pws...)
 		}
@@ -691,13 +697,8 @@ func (ddb *datadb) mergePartsFinal(pws []*partWrapper) error {
 			logger.Panicf("BUG: unexpected number of parts removed; got %d; want %d", removedParts, len(pwsChunk))
 		}
 
-		err := ddb.mergeParts(pwsChunk, true)
-		if err != nil {
-			ddb.releasePartsToMerge(pws)
-			return err
-		}
+		ddb.mustMergeParts(pwsChunk, true)
 	}
-	return nil
 }
 
 func partsToMap(pws []*partWrapper) map[*partWrapper]struct{} {
@@ -725,7 +726,7 @@ func (ddb *datadb) swapSrcWithDstParts(pws []*partWrapper, pwNew *partWrapper, d
 		switch dstPartType {
 		case partInmemory:
 			ddb.inmemoryParts = append(ddb.inmemoryParts, pwNew)
-			ddb.startInmemoryPartsFlusherLocked()
+			ddb.startOldInmemoryPartsFlusherLocked()
 		case partFile:
 			ddb.fileParts = append(ddb.fileParts, pwNew)
 		default:
@@ -840,8 +841,8 @@ func (ddb *datadb) releasePartsToMerge(pws []*partWrapper) {
 	ddb.partsLock.Unlock()
 }
 
-func (ddb *datadb) availableDiskSpace() uint64 {
-	available := fs.MustGetFreeSpace(ddb.path)
+func availableDiskSpace(path string) uint64 {
+	available := fs.MustGetFreeSpace(path)
 	reserved := atomic.LoadUint64(&reservedDiskSpace)
 	if available < reserved {
 		return 0
@@ -849,22 +850,22 @@ func (ddb *datadb) availableDiskSpace() uint64 {
 	return available - reserved
 }
 
-func (ddb *datadb) reserveDiskSpace(n uint64) bool {
-	available := fs.MustGetFreeSpace(ddb.path)
-	reserved := atomic.AddUint64(&reservedDiskSpace, n)
+func tryReserveDiskSpace(path string, n uint64) bool {
+	available := fs.MustGetFreeSpace(path)
+	reserved := reserveDiskSpace(n)
 	if available > reserved {
 		return true
 	}
-	ddb.releaseDiskSpace(n)
+	releaseDiskSpace(n)
 	return false
 }
 
-func (ddb *datadb) releaseDiskSpace(n uint64) {
-	atomic.AddUint64(&reservedDiskSpace, -n)
+func reserveDiskSpace(n uint64) uint64 {
+	return atomic.AddUint64(&reservedDiskSpace, n)
 }
 
-func (ddb *datadb) IsReadOnly() bool {
-	return atomic.LoadUint32(ddb.isReadOnly) == 1
+func releaseDiskSpace(n uint64) {
+	atomic.AddUint64(&reservedDiskSpace, ^(n - 1))
 }
 
 // reservedDiskSpace tracks global reserved disk space for currently executed
@@ -889,22 +890,13 @@ func mustCloseDatadb(ddb *datadb) {
 	ddb.wg.Wait()
 
 	// flush in-memory data to disk
-	pws := append([]*partWrapper{}, ddb.inmemoryParts...)
-	setInMergeLocked(pws)
-	err := ddb.mergePartsFinal(pws)
-	if err != nil {
-		logger.Fatalf("FATAL: cannot merge inmemory parts: %s", err)
-	}
-
-	// There is no need in using ddb.partsLock here, since nobody should acces ddb now.
-	for _, pw := range ddb.inmemoryParts {
-		pw.decRef()
-		if pw.refCount != 0 {
-			logger.Panicf("BUG: there are %d references to inmemoryPart", pw.refCount)
-		}
+	ddb.mustFlushInmemoryPartsToDisk()
+	if len(ddb.inmemoryParts) > 0 {
+		logger.Panicf("BUG: the number of in-memory parts must be zero after flushing them to disk; got %d", len(ddb.inmemoryParts))
 	}
 	ddb.inmemoryParts = nil
 
+	// close file parts
 	for _, pw := range ddb.fileParts {
 		pw.decRef()
 		if pw.refCount != 0 {
diff --git a/lib/logstorage/filters.go b/lib/logstorage/filters.go
index 168b40d547..2c75d65cff 100644
--- a/lib/logstorage/filters.go
+++ b/lib/logstorage/filters.go
@@ -2976,8 +2976,8 @@ func toUint64Clamp(f float64) uint64 {
 	if f < 0 {
 		return 0
 	}
-	if f > (1<<64)-1 {
-		return (1 << 64) - 1
+	if f > math.MaxUint64 {
+		return math.MaxUint64
 	}
 	return uint64(f)
 }
diff --git a/lib/logstorage/filters_test.go b/lib/logstorage/filters_test.go
index 289492045d..cf7d6e7827 100644
--- a/lib/logstorage/filters_test.go
+++ b/lib/logstorage/filters_test.go
@@ -9277,7 +9277,7 @@ func generateRowsFromColumns(s *Storage, tenantID TenantID, columns []column) {
 		timestamp := int64(i) * 1e9
 		lr.MustAdd(tenantID, timestamp, fields)
 	}
-	_ = s.AddRows(lr)
+	s.MustAddRows(lr)
 	PutLogRows(lr)
 }
 
@@ -9291,6 +9291,6 @@ func generateRowsFromTimestamps(s *Storage, tenantID TenantID, timestamps []int6
 		})
 		lr.MustAdd(tenantID, timestamp, fields)
 	}
-	_ = s.AddRows(lr)
+	s.MustAddRows(lr)
 	PutLogRows(lr)
 }
diff --git a/lib/logstorage/log_rows.go b/lib/logstorage/log_rows.go
index 789dab6a34..ce759b85a8 100644
--- a/lib/logstorage/log_rows.go
+++ b/lib/logstorage/log_rows.go
@@ -7,7 +7,7 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
 )
 
-// LogRows holds a set of rows needed for Storage.AddRows
+// LogRows holds a set of rows needed for Storage.MustAddRows
 //
 // LogRows must be obtained via GetLogRows()
 type LogRows struct {
diff --git a/lib/logstorage/partition.go b/lib/logstorage/partition.go
index df609c3aa3..64465de209 100644
--- a/lib/logstorage/partition.go
+++ b/lib/logstorage/partition.go
@@ -77,7 +77,7 @@ func mustOpenPartition(s *Storage, path string) *partition {
 
 	// Open datadb
 	datadbPath := filepath.Join(path, datadbDirname)
-	pt.ddb = mustOpenDatadb(pt, datadbPath, s.flushInterval, &s.isReadOnly)
+	pt.ddb = mustOpenDatadb(pt, datadbPath, s.flushInterval)
 
 	return pt
 }
diff --git a/lib/logstorage/storage.go b/lib/logstorage/storage.go
index 341ec46c18..96cf041a02 100644
--- a/lib/logstorage/storage.go
+++ b/lib/logstorage/storage.go
@@ -25,10 +25,11 @@ type StorageStats struct {
 	// PartitionsCount is the number of partitions in the storage
 	PartitionsCount uint64
 
-	PartitionStats
-
 	// IsReadOnly indicates whether the storage is read-only.
 	IsReadOnly bool
+
+	// PartitionStats contains partition stats.
+	PartitionStats
 }
 
 // Reset resets s.
@@ -51,6 +52,9 @@ type StorageConfig struct {
 	// Log entries with timestamps bigger than now+FutureRetention are ignored.
 	FutureRetention time.Duration
 
+	// MinFreeDiskSpaceBytes is the minimum free disk space at storage path after which the storage stops accepting new data.
+	MinFreeDiskSpaceBytes int64
+
 	// LogNewStreams indicates whether to log newly created log streams.
 	//
 	// This can be useful for debugging of high cardinality issues.
@@ -61,9 +65,6 @@ type StorageConfig struct {
 	//
 	// This can be useful for debugging of data ingestion.
 	LogIngestedRows bool
-
-	// MinFreeDiskSpaceBytes is the minimum free disk space at -storageDataPath after which the storage stops accepting new data
-	MinFreeDiskSpaceBytes int64
 }
 
 // Storage is the storage for log entries.
@@ -85,6 +86,9 @@ type Storage struct {
 	// futureRetention is the maximum allowed interval to write data into the future
 	futureRetention time.Duration
 
+	// minFreeDiskSpaceBytes is the minimum free disk space at path after which the storage stops accepting new data
+	minFreeDiskSpaceBytes uint64
+
 	// logNewStreams instructs to log new streams if it is set to true
 	logNewStreams bool
 
@@ -132,10 +136,6 @@ type Storage struct {
 	//
 	// It reduces the load on persistent storage during querying by _stream:{...} filter.
 	streamFilterCache *workingsetcache.Cache
-
-	isReadOnly uint32
-
-	freeDiskSpaceWatcherWG sync.WaitGroup
 }
 
 type partitionWrapper struct {
@@ -225,6 +225,11 @@ func MustOpenStorage(path string, cfg *StorageConfig) *Storage {
 		futureRetention = 24 * time.Hour
 	}
 
+	var minFreeDiskSpaceBytes uint64
+	if cfg.MinFreeDiskSpaceBytes >= 0 {
+		minFreeDiskSpaceBytes = uint64(cfg.MinFreeDiskSpaceBytes)
+	}
+
 	if !fs.IsPathExist(path) {
 		mustCreateStorage(path)
 	}
@@ -241,14 +246,15 @@ func MustOpenStorage(path string, cfg *StorageConfig) *Storage {
 	streamFilterCache := workingsetcache.New(mem / 10)
 
 	s := &Storage{
-		path:            path,
-		retention:       retention,
-		flushInterval:   flushInterval,
-		futureRetention: futureRetention,
-		logNewStreams:   cfg.LogNewStreams,
-		logIngestedRows: cfg.LogIngestedRows,
-		flockF:          flockF,
-		stopCh:          make(chan struct{}),
+		path:                  path,
+		retention:             retention,
+		flushInterval:         flushInterval,
+		futureRetention:       futureRetention,
+		minFreeDiskSpaceBytes: minFreeDiskSpaceBytes,
+		logNewStreams:         cfg.LogNewStreams,
+		logIngestedRows:       cfg.LogIngestedRows,
+		flockF:                flockF,
+		stopCh:                make(chan struct{}),
 
 		streamIDCache:     streamIDCache,
 		streamTagsCache:   streamTagsCache,
@@ -298,7 +304,6 @@ func MustOpenStorage(path string, cfg *StorageConfig) *Storage {
 
 	s.partitions = ptws
 	s.runRetentionWatcher()
-	s.startFreeDiskSpaceWatcher(uint64(cfg.MinFreeDiskSpaceBytes))
 	return s
 }
 
@@ -368,7 +373,6 @@ func (s *Storage) MustClose() {
 	// Stop background workers
 	close(s.stopCh)
 	s.wg.Wait()
-	s.freeDiskSpaceWatcherWG.Wait()
 
 	// Close partitions
 	for _, pw := range s.partitions {
@@ -401,12 +405,11 @@ func (s *Storage) MustClose() {
 	s.path = ""
 }
 
-// AddRows adds lr to s.
-func (s *Storage) AddRows(lr *LogRows) error {
-	if s.IsReadOnly() {
-		return errReadOnly
-	}
-
+// MustAddRows adds lr to s.
+//
+// It is recommended checking whether the s is in read-only mode by calling IsReadOnly()
+// before calling MustAddRows.
+func (s *Storage) MustAddRows(lr *LogRows) {
 	// Fast path - try adding all the rows to the hot partition
 	s.partitionsLock.Lock()
 	ptwHot := s.ptwHot
@@ -419,7 +422,7 @@ func (s *Storage) AddRows(lr *LogRows) error {
 		if ptwHot.canAddAllRows(lr) {
 			ptwHot.pt.mustAddRows(lr)
 			ptwHot.decRef()
-			return nil
+			return
 		}
 		ptwHot.decRef()
 	}
@@ -463,7 +466,6 @@ func (s *Storage) AddRows(lr *LogRows) error {
 		ptw.decRef()
 		PutLogRows(lrPart)
 	}
-	return nil
 }
 
 var tooSmallTimestampLogger = logger.WithThrottler("too_small_timestamp", 5*time.Second)
@@ -532,44 +534,14 @@ func (s *Storage) UpdateStats(ss *StorageStats) {
 		ptw.pt.updateStats(&ss.PartitionStats)
 	}
 	s.partitionsLock.Unlock()
+
 	ss.IsReadOnly = s.IsReadOnly()
 }
 
-// IsReadOnly returns information is storage in read only mode
+// IsReadOnly returns true if s is in read-only mode.
 func (s *Storage) IsReadOnly() bool {
-	return atomic.LoadUint32(&s.isReadOnly) == 1
-}
-
-func (s *Storage) startFreeDiskSpaceWatcher(freeDiskSpaceLimitBytes uint64) {
-	f := func() {
-		freeSpaceBytes := fs.MustGetFreeSpace(s.path)
-		if freeSpaceBytes < freeDiskSpaceLimitBytes {
-			// Switch the storage to readonly mode if there is no enough free space left at s.path
-			logger.Warnf("switching the storage at %s to read-only mode, since it has less than -storage.minFreeDiskSpaceBytes=%d of free space: %d bytes left",
-				s.path, freeDiskSpaceLimitBytes, freeSpaceBytes)
-			atomic.StoreUint32(&s.isReadOnly, 1)
-			return
-		}
-		if atomic.CompareAndSwapUint32(&s.isReadOnly, 1, 0) {
-			logger.Warnf("enabling writing to the storage at %s, since it has more than -storage.minFreeDiskSpaceBytes=%d of free space: %d bytes left",
-				s.path, freeDiskSpaceLimitBytes, freeSpaceBytes)
-		}
-	}
-	f()
-	s.freeDiskSpaceWatcherWG.Add(1)
-	go func() {
-		defer s.freeDiskSpaceWatcherWG.Done()
-		ticker := time.NewTicker(time.Second)
-		defer ticker.Stop()
-		for {
-			select {
-			case <-s.stopCh:
-				return
-			case <-ticker.C:
-				f()
-			}
-		}
-	}()
+	available := fs.MustGetFreeSpace(s.path)
+	return available > s.minFreeDiskSpaceBytes
 }
 
 func (s *Storage) debugFlush() {
diff --git a/lib/logstorage/storage_search_test.go b/lib/logstorage/storage_search_test.go
index d61035a5dc..63404838ce 100644
--- a/lib/logstorage/storage_search_test.go
+++ b/lib/logstorage/storage_search_test.go
@@ -70,7 +70,7 @@ func TestStorageRunQuery(t *testing.T) {
 					})
 					lr.MustAdd(tenantID, timestamp, fields)
 				}
-				_ = s.AddRows(lr)
+				s.MustAddRows(lr)
 				PutLogRows(lr)
 			}
 		}
@@ -366,7 +366,7 @@ func TestStorageSearch(t *testing.T) {
 					})
 					lr.MustAdd(tenantID, timestamp, fields)
 				}
-				_ = s.AddRows(lr)
+				s.MustAddRows(lr)
 				PutLogRows(lr)
 			}
 		}
diff --git a/lib/logstorage/storage_test.go b/lib/logstorage/storage_test.go
index 9951a6a4c5..193179bb17 100644
--- a/lib/logstorage/storage_test.go
+++ b/lib/logstorage/storage_test.go
@@ -32,7 +32,7 @@ func TestStorageMustAddRows(t *testing.T) {
 		lr := newTestLogRows(1, 1, 0)
 		lr.timestamps[0] = time.Now().UTC().UnixNano()
 		totalRowsCount += uint64(len(lr.timestamps))
-		_ = s.AddRows(lr)
+		s.MustAddRows(lr)
 		sStats.Reset()
 		s.UpdateStats(&sStats)
 		if n := sStats.RowsCount(); n != totalRowsCount {
@@ -56,7 +56,7 @@ func TestStorageMustAddRows(t *testing.T) {
 		lr.timestamps[i] = time.Now().UTC().UnixNano()
 	}
 	totalRowsCount += uint64(len(lr.timestamps))
-	_ = s.AddRows(lr)
+	s.MustAddRows(lr)
 	sStats.Reset()
 	s.UpdateStats(&sStats)
 	if n := sStats.RowsCount(); n != totalRowsCount {
@@ -80,7 +80,7 @@ func TestStorageMustAddRows(t *testing.T) {
 		now += nsecPerDay
 	}
 	totalRowsCount += uint64(len(lr.timestamps))
-	_ = s.AddRows(lr)
+	s.MustAddRows(lr)
 	sStats.Reset()
 	s.UpdateStats(&sStats)
 	if n := sStats.RowsCount(); n != totalRowsCount {