Robert Milkowski wrote:
PvdZ> This could be related to Linux trading reliability for speed by doing
PvdZ> async metadata updates.
PvdZ> If your system crashes before your metadata is flushed to disk your
PvdZ> filesystem might be hosed and a restore
PvdZ> from backups may be needed.
you can achieve something similar with fastfs on ufs file systems and
setting zil_disable to 1 on ZFS.
No, zil_disable does not trade off consistency for performance the way
'fastfs' on ufs or async metadata updates on EXT do!
Setting zil_disable causes ZFS to not push synchronous operations (eg,
fsync(), O_DSYNC, NFS ops) to disk immediately, but it does not
compromise filesystem integrity in any way. Unlike these other
filesystems "fast" modes, ZFS (even with zil_disable=1) will not corrupt
itself and send you to backup tapes.
To state it another way, setting 'zil_disable=1' on ZFS will at worst
cause some operations which requested synchronous semantics to not
actually be on disk in the event of a crash, whereas other filesystems
can corrupt themselves and lose all your data.
All that said, 'zil_disable' is a completely unsupported hack, and
subject to change at any time. It will probably eventually be replaced
by 6280630 "zil synchronicity".
--matt
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