Dear experts,
when migrating from a 6 disk to a 4 disk raidz1 zpool with 'zfs send -R|zfs
receive', the system's response time dropped noticeably.
The run queue increased to 28-32, and 'prstat -Lm' showed that several system
threads were locked repeatedly - noticeably fmd, devfsd and many of the
svc.{configd,startd}.
The system is an E4500 with 4 US II CPU, so I added 6 CPU on the fly which
helped a bit but the run queue was still about 10. Reasonably, things were
worst when the migration was processing gzip-compressed FS's, but surprisingly
the run queue was >2 with uncompressed FS's, too.
OS is SXDE snv79b.
2nd observation was that even when copying gzip'ed FS's, the CPUs had about 30%
idle cycles
and zero wio%.
How come? Is this (locking of system threads -> increased run queue) a bug or
expected behaviour?
3rd: The zpool property 'delegation' was not copied. Same Q: bug or expected?
Note: migration
was from zpool version 8 to zpool version 10.
4th: Performance was way beyond my expectations. I set up regular recursive
snapshots via cron,
so every FS had many (42) snapshots, many empty or of small size. Even the
empty snaps took
5 seconds each (34 bytes/5 sec), and max. throughput was 8 MB/s with the few
snaps that had
some GB of data. I understand that even to copy an empty snapshot needs some
time to process,
and I guess the reason for the poor performance is the locking described above.
Still the same Q
arises: Is a max. throughput of 8 MB/s to write to a raidz1 of 4 FC disks ok
with send/receive?
Workaround: If you recursively send/receive a zpool with many snapshots,
consider to decrease
the # of snapshots first. E.g. when you have rotating snapshots like every 10
minutes
([EMAIL PROTECTED],min-10,min-20,...} and every hour ([EMAIL
PROTECTED],hourly-01,...}, delete these
snapshots prior to the send/receive operation.
Thanks in advance, Paul
This message posted from opensolaris.org
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
