[Beowulf] Software RAID?
smulcahy at aplpi.com
Wed Nov 28 00:35:52 PST 2007
Bernd Schubert wrote:
> I don't know about other hardware raid cards, but for 3ware cards you should
> always use a BBU, even if your system DOES have an UPS.
> We did have the unlucky setup to use 9500S cards only for software raid. Now
> after about 3 years in production usage the hard disks grew older and sectors
> did/do fail more often. The 3ware driver now has the very nice behaviour to
> reset the entire card with every sectors that can't be read. If you now do
> have disk-write cache enabled and you don't have a BBU, you will loose all
> the unwritten data in the cache due to this reset... As you might expect,
> your underlying filesystem won't like this unexpected data loss...
> If you now decide to disable the controller write cache, you get another
> suprise - write performance per disk goes down to 3-9 MB/s (from around 50
> MB/s for our disks). The 3ware controller has the nice feature to control
> both, its own cache and the cache of the disk, there's no way to disable only
> the controllers cache.
Ouch. Thanks for the heads up.
-stephen.goes to order a 3ware bbu
Stephen Mulcahy, Applepie Solutions Ltd., Innovation in Business Center,
GMIT, Dublin Rd, Galway, Ireland. +353.91.751262 http://www.aplpi.com
Registered in Ireland, no. 289353 (5 Woodlands Avenue, Renmore, Galway)
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