topic Re: iSCSI write performance issue RHEL4 in Operating System - Linux

iSCSI write performance issue RHEL4

David Nixon — Wed, 27 Jan 2010 11:32:08 GMT

Hello All.
Been seeing truly dire synchronous write
performance - 250KBs - whilst testing an iSCSI RAID with RHEL4.8.
Can write to the
same RAID at ~80GBs from a RHEL5.2 system.

The RAID in question is an Arena-MaxTronic SS-6603S. About 10% of TCP segments are retransmitted during these writes and there
are 6-8 second pauses between disc activity.
The max_xmit_data_segement_len is always 16k - which seems low.

Has anyone has come across such incompatibilities when using the RHEL4 Open-iSCSI driver?

Re: iSCSI write performance issue RHEL4

Steven E. Protter — Wed, 27 Jan 2010 13:46:59 GMT

Shalom,

I suspect this is a configuration issue on the OS.

You will need to tweak settings in /proc to make this work right. Then save them in sysctl.

Use RHEL 5.2 as your guidepost, but keep track of what you do and post back.

SEP

Re: iSCSI write performance issue RHEL4

Alan_152 — Thu, 28 Jan 2010 15:55:32 GMT

What kernel and iSCSI revisions are you using?

Re: iSCSI write performance issue RHEL4

David Nixon — Thu, 28 Jan 2010 16:30:09 GMT

The Kernel at update 8 is 2.6.9-89. I
don't recall mention of iSCSI in the release notes
so the initiator may be much the same as in earlier
updates.

The utilities are: iscsi-initiator-utils-4.03.0-8

Re: iSCSI write performance issue RHEL4

Alan_152 — Thu, 28 Jan 2010 23:13:04 GMT

open-iscsi is currently at 2.0.871. The latest stable kernel is 2.6.32.6. Every time I've worked with iscsi, I had to upgrade to latest/greatest to get anything to work right.

Re: iSCSI write performance issue RHEL4

David Nixon — Fri, 05 Feb 2010 11:05:13 GMT

The issue is with use of the bond driver
to connect to this particular RAID box; via
a dual port NIC.

The default Round Robin policy for transmitting packets is resulting in retransmissions.

Re: iSCSI write performance issue RHEL4

David Nixon — Fri, 05 Feb 2010 15:41:31 GMT

Default operation mode of Linux bond driver
unsuitable for a multiported iSCSI RAID - experiment with other bonding policies.