I'm working with a Cyrus IMAP server running on a T2000 box under
Solaris 10 10/09 with current patches. Mailboxes reside on six ZFS
filesystems, each containing about 200 gigabytes of data. These are
part of a single zpool built on four Iscsi devices from our Netapp
filer.
One of these ZFS filesystems contains a number of global and per-user
databases in addition to one sixth of the mailboxes. I'm thinking of
moving these databases to a separate ZFS filesystem. Access to these
databases must be quick to ensure responsiveness of the server. We
are currently experiencing a slowdown in performance when the number
of simultaneous IMAP sessions rises above 3000. These databases are
opened and memory-mapped by all processes. They have the usual
requirement for locking and synchronous writes whenever they are
updated.
Is moving the databases (IMAP metadata) to a separate ZFS filesystem
likely to improve performance? I've heard that this is important, but
I'm not clear why this is. Does each filesystem have its own queue in
the ARC or ZIL? Here are some statistics taken while the server was
busy and access was slow:
# /usr/local/sbin/zilstat 5 5
N-Bytes N-Bytes/s N-Max-Rate B-Bytes B-Bytes/s B-Max-Rate ops <=4kB
4-32kB >=32kB
1126664 225332 515872 11485184 2297036 3469312 292 163
51 79
740536 148107 250896 9535488 1907097 4005888 198 106
24 68
758344 151668 179104 12546048 2509209 2682880 227 93
45 89
603304 120660 204344 9179136 1835827 2084864 179 89
23 67
948896 189779 346520 15880192 3176038 4173824 262 108
32 123
# /usr/local/sbin/arcstat 5 5
Time read miss miss% dmis dm% pmis pm% mmis mm% arcsz c
10:50:16 191M 31M 16 14M 8 17M 48 18M 12 30G 32G
10:50:21 1K 148 10 76 5 72 58 78 15 30G 32G
10:50:26 1K 154 12 88 7 65 72 96 18 30G 32G
10:50:31 796 61 7 54 7 6 35 25 8 30G 32G
10:50:36 1K 117 9 105 8 12 53 44 10 30G 32G
--
-Gary Mills- -Unix Group- -Computer and Network Services-
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