diff --git a/sync.go b/sync.go
index fa9c1d9..0f6e719 100644
--- a/sync.go
+++ b/sync.go
@@ -21,7 +21,7 @@ import (
 
 const SyncBlockBits = 28
 const SyncBlockMask = (rdx.ID(1) << SyncBlockBits) - 1
-const MaxParcelSize = 5_000_000 // 5MB
+const MaxParcelSize = 100_000_000
 
 type SyncHost interface {
 	protocol.Drainer
@@ -213,7 +213,7 @@ func (sync *Syncer) Feed(ctx context.Context) (recs protocol.Records, err error)
 			return
 		case <-sync.WaitDrainState(ctx, SendDiff):
 		}
-		recs, err = sync.FeedBlockDiff()
+		recs, err = sync.FeedBlockDiff(ctx)
 		if err == io.EOF {
 			recs2, _ := sync.FeedDiffVV()
 			recs = append(recs, recs2...)
@@ -384,7 +384,7 @@ func (sync *Syncer) nextBlockDiff() (bool, rdx.VV, error) {
 	return true, sendvv, nil
 }
 
-func (sync *Syncer) FeedBlockDiff() (diff protocol.Records, err error) {
+func (sync *Syncer) FeedBlockDiff(ctx context.Context) (diff protocol.Records, err error) {
 	hasChanges, sendvv, cerr := sync.nextBlockDiff()
 	if cerr != nil {
 		return nil, cerr
@@ -409,13 +409,20 @@ func (sync *Syncer) FeedBlockDiff() (diff protocol.Records, err error) {
 		lim, ok := sendvv[id.Src()]
 		if ok && (id.Pro() > lim || lim == 0) {
 			parcel = append(parcel, protocol.Record('F', rdx.ZipUint64(uint64(id-block)))...)
-			parcel = append(parcel, protocol.Record(rdt, sync.ffit.Value())...)
+			val := sync.ffit.Value()
+			parcel = append(parcel, protocol.Record(rdt, val)...)
+			if len(val) > MaxParcelSize {
+				sync.log.WarnCtx(sync.logCtx(ctx), "too big key size", len(val))
+			}
 			continue
 		}
 		diff := rdx.Xdiff(rdt, sync.ffit.Value(), sendvv)
 		if len(diff) != 0 {
 			parcel = append(parcel, protocol.Record('F', rdx.ZipUint64(uint64(id-block)))...)
 			parcel = append(parcel, protocol.Record(rdt, diff)...)
+			if len(diff) > MaxParcelSize {
+				sync.log.WarnCtx(sync.logCtx(ctx), "too big diff size", len(diff))
+			}
 		}
 	}
 	protocol.CloseHeader(parcel, bmark)