On 2010-08-23 15:58, Ric Wheeler wrote: > On 08/23/2010 08:48 AM, Christoph Hellwig wrote: >> On Mon, Aug 23, 2010 at 02:30:33PM +0200, Tejun Heo wrote: >>> It might be useful to give several example configurations with >>> different cache configurations. I don't have much experience with >>> battery backed arrays but aren't they suppose to report write through >>> cache automatically? >> >> They usually do. I have one that doesn't, but SYNCHRONIZE CACHE on >> it is so fast that it effectively must be a no-op. >> > > Arrays are not a problem in general - they normally have internally, redundant > batteries to hold up the cache. > > The issue is when you have an internal hardware RAID card with a large cache. > Those cards sit in your server and the batteries on the card protect its > internal cache, but do not have the capacity to hold up the drives behind it. > > Normally, those drives should have their write cache disabled, but sometimes > (especially with S-ATA disks) this is not done. The problem purely exists on arrays that report write back cache enabled AND don't implement SYNC_CACHE as a noop. Do any of them exist, or are they purely urban legend? -- Jens Axboe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
