On Wed, 16 Jan 2013, Thomas Nau wrote:

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)

If almost all of the I/Os are 4K, maybe your ZVOLs should use a volblocksize of 4K? This seems like the most obvious improvement.

[ stuff removed ]

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?

Matching the volume block size to what the clients are actually using (due to their filesystem configuration) should improve performance during normal operations and should reduce the number of blocks which need to be sent in the backup by reducing write amplification due to "overlap" blocks..

Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
zfs-discuss mailing list

Reply via email to