Bryan Murphy wrote:
Our database server connects to the san via iSCSI over Gig/E using
jumbo frames. File system is XFS (noatime).

Throughput, however, kinda sucks. I just can't get the kind of
throughput to it I was hoping to get. When our memory cache is blown,
the database can be downright painful for the next few minutes as
everything gets paged back into the cache.

Remember that Gig/E is bandwidth limited to about 100 Mbyte/sec. Maybe
a little faster than that downhill with a tailwind, but not much.
You're going to get much better bandwidth connecting to a local raid
card talking to local disks simply due to not having the ethernet as a
bottleneck. iSCSI is easy to set up and manage, but it's slow. This is
the big advantage Fibre Channel has- serious performance. You can have
multiple channels on a single fibre channel card- IIRC, QLogic's cards
have a default of 4 channels- each pumping 400 Mbyte/sec. At which
point the local bus rapidly becomes the bottleneck. Of course, this
comes at the cost of a signifigant increase in complexity.


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