Matthew Ahrens wrote On 10/16/06 09:07,:
Robert Milkowski wrote:
Hello zfs-discuss,
S10U2+patches. ZFS pool of about 2TB in size. Each day snapshot is
created and 7 copies are kept. There's quota set for a file system
however there's always at least 50GB of free space in a file system
(and much more in a pool). ZFS file system is exported over NFS.
Snapshots consume about 280GB of space.
We have noticed so performance problems on nfs clients to this file
system even during times with smaller load. Rising quota didn't
help. However removing oldest snapshot automatically solved
performance problems.
I do not have more details - sorry.
Is it expected for snapshots to have very noticeable performance
impact on file system being snapshoted?
No, this behavior is unexpected. The only way that snapshots should
have a performance impact on access to the filesystem is if you are
running low on space in the pool or quota (which it sounds like you are
not).
Can you describe what the performance problems were? What was the
workload like? What problem did you identify? How did it improve when
you 'zfs destroy'-ed the oldest snapshot? Are you sure that the oldest
snapshot wasn't pushing you close to your quota?
--matt
I could well believe there would be a hiccup when the snapshot is
taken on the rest of the pool. Each snapshot calls txg_wait_synced
four times. A few related to the zil and one from dsl_sync_task_group_wait
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