iSCSI write performance issue RHEL4

[David Nixon]

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?

[Steven E. Protter]

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

[Alan_152]

What kernel and iSCSI revisions are you using?

[David Nixon]

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

[Alan_152]

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.

[David Nixon]

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.

[David Nixon]

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