Document that hole_birth is effectively useless

The first sentence of this commit comes from the wiki, and was
originally written by:
Rich Ercolani <rincebrain@gmail.com>
with changes by:
Tom Caputi <tcaputi@datto.com>

Reviewed-by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Laager <rlaager@wiktel.com>
Closes #8641
Closes #8642
This commit is contained in:
Richard Laager 2019-04-18 20:21:09 -05:00 committed by Brian Behlendorf
parent 6ce7b2d9ad
commit 063edd7fd8

View File

@ -383,6 +383,14 @@ READ\-ONLY COMPATIBLE no
DEPENDENCIES enabled_txg
.TE
This feature has/had bugs, the result of which is that, if you do a
\fBzfs send -i\fR (or \fB-R\fR, since it uses \fB-i\fR) from an affected
dataset, the receiver will not see any checksum or other errors, but the
resulting destination snapshot will not match the source. Its use by
\fBzfs send -i\fR has been disabled by default. See the
\fBsend_holes_without_birth_time\fR module parameter in
zfs-module-parameters(5).
This feature improves performance of incremental sends (\fBzfs send -i\fR)
and receives for objects with many holes. The most common case of
hole-filled objects is zvols.