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Re: Dell RAID device support?

On Tue, 22 Nov 2011, Roger Pau Monné wrote:

Forgot to say, but you can find more info about the SAS 6/iR RAID
problems in this thread:

And it will be great if you can port a newer driver that has better
support for this card.

I don't have experience with the M610 blade, but I did look at the RAID performance on an M600 blade.

The first problem is that the blade does not appear to have a battery-backed cache, and the write cache for any raid volumes is not enabled. There's nothing in the BIOS setup to enable it, but there is a Linux program, lsiutil, available that can enable the write caching on the raid volumes. That help the write performance considerably. I booted a Knoppix live CD and used that to build the lsiutil program and run it.

Another consideration which I have not been able to look into is that NetBSD will only send one command at a time to each drive if the drive does not indicate that tagged queueing is availble. The message referenced above does not seem to indicate that tagged queueing is enabled for the drives, and that may also impact performance. I've been waiting to get access to an M600 blade to test this, but it hasn't been available for me to play with yet. I bring this up because I found that the Compaq/HP SmartArray controller had this issue, and once I fixed the driver to indicate that tagged queueing was available, performance with no write caching improved when used with softdep or wapbl mounts.

Michael L. Hitch              
Computer Consultant
Information Technology Center
Montana State University        Bozeman, MT     USA

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