Re: [OT] RAID controllers blocking one another?

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On Thu, 17 Jan 2008, Sean Davis wrote:

We have a machine that serves as a fileserver and a database server.  Our
server hosts a raid array of 40 disk drives, attached to two3-ware cards,
one 9640SE-24 and one 9640SE-16. We have noticed that activity on one
controller blocks access on the second controller, not only for disk-IO but
also the command line tools which become unresponsive for the inactive
controller.   The controllers are sitting in adjacent PCI-express slots on a
machine with dual-dual AMD and 16GB of RAM.  Has anyone else noticed issues
like this?  Throughput for either controller is a pretty respectable
150-200MB/s writing and somewhat faster for reading, but the "blocking" is
problematic, as the machine is serving multiple purposes.

I know this is off-topic, but I know lots of folks here deal with very large
disk arrays; it is hard to get real-world input on machines such as these.

there have been a lot of discussions on the linux-kernel mailing list over the last several months on the topic of IO to one set of drives interfearing with IO to another set of drives. The soon-to-be-released 2.6.24 kernel includes a substantial amount of work in this area that (at least on initial reports) is showing significant improvements.

I haven't had the time to test this out yet, so I can't add personal experiance, but it's definantly something to look at on a test system.

David Lang

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