Gary Mills wrote:
We have an IMAP e-mail server running on a Solaris 10 10/09 system.
It uses six ZFS filesystems built on a single zpool with 14 daily
snapshots. Every day at 11:56, a cron command destroys the oldest
snapshots and creates new ones, both recursively. For about four
minutes thereafter, the load average drops and I/O to the disk devices
drops to almost zero. Then, the load average shoots up to about ten
times normal and then declines to normal over about four minutes, as
disk activity resumes. The statistics return to their normal state
about ten minutes after the cron command runs.
Is it destroying old snapshots or creating new ones that causes this
dead time? What does each of these procedures do that could affect
the system? What can I do to make this less visible to users?
I have a couple of Solaris 10 boxes that do something similar (hourly
snaps) and I've never seen any lag in creating and destroying
snapshots. One system with 16 filesystems takes 5 seconds to destroy
the 16 oldest snaps and create 5 recursive new ones. I logged load
average on these boxes and there is a small spike on the hour, but this
is down to sending the snaps, not creating them.
--
Ian.
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