Re: [OT] RAID controllers blocking one another?

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