This is what it buys you: 1. I/O is better spread across multiple drive heads. Not so important for writes, if you have a good-sized write-cache, but especially helpful for reads. TSM does not do round-robin allocation of DB pages across it's volumes. It fills up one, then works on the next. Even if you have gotten to the point where you have multiple dbvols, you'll tend to allocate pages for a node together on the same dbvol at first. Then when you go to reference them, you'll be hitting one drive more than the others. RAID5 will do a reasonable job of spreading things across multiple heads.
2. FAStTs have a nice feature where they will automatically replace a failed drive with a hot spare. Then you can replace the hot-spare drive at your leisure. Without this, if you were using single LUNs and one failed, you would have to replace the failed drive, then re-mirror within TSM. Not nearly as automatic and your window of exposure will be greater. In our shop, we have separated management of the FAStT devices from management of the TSM environment (i.e., different staff), so it is particularly attractive to the folks who manage the FAStT boxes to just have hot-spare coverage for everything. Then they don't have to worry about the impact on TSM when a drive fails. At 03:40 PM 1/20/2006, Jack Coats wrote:
Just curious, and playing a little devils advocate, but does it buy anything to mirror over raid5? Wouldn't it be more efficient (processor on the san, and storage) just to put volumes out there and let TSM manage them? You would want to have the mirrored volumes on separate physical drives (preferably in different trays, etc) also.
-- Paul Zarnowski Ph: 607-255-4757 Manager, Storage Systems Fx: 607-255-8521 719 Rhodes Hall, Ithaca, NY 14853-3801 Em: [EMAIL PROTECTED]
