Illumos #3104: eliminate empty bpobjs

3104 eliminate empty bpobjs
Reviewed by: George Wilson <[email protected]>
Reviewed by: Adam Leventhal <[email protected]>
Reviewed by: Christopher Siden <[email protected]>
Reviewed by: Garrett D'Amore <[email protected]>
Approved by: Eric Schrock <[email protected]>

References:
  illumos/illumos-gate@f17457368189aa911f774c38c1f21875a568bdca
  illumos changeset: 13782:8f78aae28a63
  https://www.illumos.org/issues/3104

Ported-by: Brian Behlendorf <[email protected]>

1 files changed, 28 insertions, 0 deletions

diff --git a/man/man5/zpool-features.5 b/man/man5/zpool-features.5
index 3c1930c35..0ab179ef7 100644
--- a/man/man5/zpool-features.5
+++ b/man/man5/zpool-features.5
@@ -169,5 +169,33 @@ through the \fBfreeing\fR property.
 
 This feature is only \fBactive\fR while \fBfreeing\fR is non\-zero.
 .RE
+
+.sp
+.ne 2
+.na
+\fB\fBempty_bpobj\fR\fR
+.ad
+.RS 4n
+.TS
+l l .
+GUID	com.delphix:empty_bpobj
+READ\-ONLY COMPATIBLE	yes
+DEPENDENCIES	none
+.TE
+
+This feature increases the performance of creating and using a large
+number of snapshots of a single filesystem or volume, and also reduces
+the disk space required.
+
+When there are many snapshots, each snapshot uses many Block Pointer
+Objects (bpobj's) to track blocks associated with that snapshot.
+However, in common use cases, most of these bpobj's are empty.  This
+feature allows us to create each bpobj on-demand, thus eliminating the
+empty bpobjs.
+
+This feature is \fBactive\fR while there are any filesystems, volumes,
+or snapshots which were created after enabling this feature.
+.RE
+
 .SH "SEE ALSO"
 \fBzpool\fR(1M)