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Illumos 4370, 4371

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4370 avoid transmitting holes during zfs send
4371 DMU code clean up

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
Approved by: Garrett D'Amore <garrett@damore.org>a

References:
  https://www.illumos.org/issues/4370
  https://www.illumos.org/issues/4371
  https://github.com/illumos/illumos-gate/commit/43466aa

Ported by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2529
This commit is contained in:
Max Grossman
2013-12-09 10:37:51 -08:00
committed by Brian Behlendorf
parent fa86b5dbb6
commit b0bc7a84d9
32 changed files with 690 additions and 385 deletions
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man/man5/zpool-features.5
+65
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@@ -273,5 +273,70 @@ this feature are destroyed.
.RE
.sp
.ne 2
.na
\fB\fBenabled_txg\fR\fR
.ad
.RS 4n
.TS
l l .
GUID com.delphix:enabled_txg
READ\-ONLY COMPATIBLE yes
DEPENDENCIES none
.TE
Once this feature is enabled ZFS records the transaction group number
in which new features are enabled. This has no user-visible impact,
but other features may depend on this feature.
This feature becomes \fBactive\fR as soon as it is enabled and will
never return to being \fBenabled\fB.
.RE
.sp
.ne 2
.na
\fB\fBhole_birth\fR\fR
.ad
.RS 4n
.TS
l l .
GUID com.delphix:hole_birth
READ\-ONLY COMPATIBLE no
DEPENDENCIES enabled_txg
.TE
This feature improves performance of incremental sends ("zfs send -i")
and receives for objects with many holes. The most common case of
hole-filled objects is zvols.
An incremental send stream from snapshot \fBA\fR to snapshot \fBB\fR
contains information about every block that changed between \fBA\fR and
\fBB\fR. Blocks which did not change between those snapshots can be
identified and omitted from the stream using a piece of metadata called
the 'block birth time', but birth times are not recorded for holes (blocks
filled only with zeroes). Since holes created after \fBA\fR cannot be
distinguished from holes created before \fBA\fR, information about every
hole in the entire filesystem or zvol is included in the send stream.
For workloads where holes are rare this is not a problem. However, when
incrementally replicating filesystems or zvols with many holes (for
example a zvol formatted with another filesystem) a lot of time will
be spent sending and receiving unnecessary information about holes that
already exist on the receiving side.
Once the \fBhole_birth\fR feature has been enabled the block birth times
of all new holes will be recorded. Incremental sends between snapshots
created after this feature is enabled will use this new metadata to avoid
sending information about holes that already exist on the receiving side.
This feature becomes \fBactive\fR as soon as it is enabled and will
never return to being \fBenabled\fB.
.RE
.SH "SEE ALSO"
\fBzpool\fR(8)