[Beowulf] Software RAID?

stephen mulcahy 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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