Dear all
I've a question concerning possible performance tuning for both iSCSI access
and replicating a ZVOL through zfs send/receive. We export ZVOLs with the
default volblocksize of 8k to a bunch of Citrix Xen Servers through iSCSI.
The pool is made of SAS2 disks (11 x 3-way mirrored) plus mirrored STEC RAM ZIL
SSDs and 128G of main memory
The iSCSI access pattern (1 hour daytime average) looks like the following
(Thanks to Richard Elling for the dtrace script)
R
value ------------- Distribution ------------- count
256 | 0
512 |@ 22980
1024 | 663
2048 | 1075
4096 |@@@@@@@@@@@@@@@@@@@@@@@@@ 433819
8192 |@@ 40876
16384 |@@ 37218
32768 |@@@@@ 82584
65536 |@@ 34784
131072 |@ 25968
262144 |@ 14884
524288 | 69
1048576 | 0
W
value ------------- Distribution ------------- count
256 | 0
512 |@ 35961
1024 | 25108
2048 | 10222
4096 |@@@@@@@@@@@@@@@@@@@@@@@ 1243634
8192 |@@@@@@@@@ 521519
16384 |@@@@ 218932
32768 |@@@ 146519
65536 | 112
131072 | 15
262144 | 78
524288 | 0
For disaster recovery we plan to sync the pool as often as possible
to a remote location. Running send/receive after a day or so seems to take
a significant amount of time wading through all the blocks and we hardly
see network average traffic going over 45MB/s (almost idle 1G link).
So here's the question: would increasing/decreasing the volblocksize improve
the send/receive operation and what influence might show for the iSCSI side?
Thanks for any help
Thomas
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