Prevent ZFS leaking pool free space #2896
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When processing async destroys ZFS would leak space every txg timeout
(5 seconds by default), if no writes occurred, until the pool is totally
full. At this point it would be unfixable without a pool recreation.
In addition if the machine was rebooted with the pool in this situation
would fail to import on boot, hanging indefinitely, as the import process
requires the ability to write data to the pool. Any attempts to query
the pool status during the hung import would not return as the import
holds the pool lock.
The only way to import such a pool would be to specify -o readonly=on
to the zpool import.
zdb -bb <pool> can be used to check for "deferred free" size which is
where this lost space will be counted.
Ported by: Tim Chase <tim@chase2k.com>
References:
freebsd/freebsd-src@48431b7
http://svnweb.freebsd.org/base?view=revision&revision=273158
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I came across this awhile ago and have been meaning to post it for some feedback as a pull request. |
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@ahrens could you comment on this recent bug fix from freebsd. |
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@behlendorf The fix in FreeBSD is correct. I have a more comprehensive change in this area coming to illumos. These changes are out for review: https://reviews.csiden.org/r/132/ |
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@ahrens Thanks for the review. For the moment we've picked up the FreeBSD fix, we'll replace it with the more comprehensive fix once it's ready. |
ryao
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Nov 29, 2014
When processing async destroys ZFS would leak space every txg timeout (5 seconds by default), if no writes occurred, until the pool is totally full. At this point it would be unfixable without a pool recreation. In addition if the machine was rebooted with the pool in this situation would fail to import on boot, hanging indefinitely, as the import process requires the ability to write data to the pool. Any attempts to query the pool status during the hung import would not return as the import holds the pool lock. The only way to import such a pool would be to specify -o readonly=on to the zpool import. zdb -bb <pool> can be used to check for "deferred free" size which is where this lost space will be counted. References: freebsd/freebsd-src@48431b7 http://svnweb.freebsd.org/base?view=revision&revision=273158 https://reviews.csiden.org/r/132/ Porting notes: This issue was filed as illumos 5347 and a more comprehensive fix is under review. Once that change is finalized it will be integrated, in the meanwhile the FreeBSD fix has been merged to prevent the issue. Ported by: Tim Chase <tim@chase2k.com> Signed-off-by: Matthew Ahrens mahrens@delphix.com Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#2896
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When processing async destroys ZFS would leak space every txg timeout
(5 seconds by default), if no writes occurred, until the pool is totally
full. At this point it would be unfixable without a pool recreation.
In addition if the machine was rebooted with the pool in this situation
would fail to import on boot, hanging indefinitely, as the import process
requires the ability to write data to the pool. Any attempts to query
the pool status during the hung import would not return as the import
holds the pool lock.
The only way to import such a pool would be to specify -o readonly=on
to the zpool import.
zdb -bb can be used to check for "deferred free" size which is
where this lost space will be counted.
Ported by: Tim Chase tim@chase2k.com
References:
freebsd/freebsd-src@48431b7
http://svnweb.freebsd.org/base?view=revision&revision=273158