Messages in this thread | | | Date | Thu, 3 Sep 2009 07:35:14 -0700 (PDT) | From | david@lang ... | Subject | Re: raid is dangerous but that's secret (was Re: [patch] ext2/3: document conditions when reliable operation is possible) |
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On Thu, 3 Sep 2009, Krzysztof Halasa wrote:
> Ric Wheeler <rwheeler@redhat.com> writes: > >>>> Just to add some support to this, all of the external RAID arrays that >>>> I know of normally run with write cache disabled on the component >>>> drives. >>> >>> Do they use "off the shelf" SATA (or PATA) disks, and if so, which ones? >> >> Which drives various vendors ships changes with specific products. >> Usually, they ship drives that have carefully vetted firmware, etc. >> but they are close to the same drives you buy on the open market. > > But they aren't the same, are they? If they are not, the fact they can > run well with the write-through cache doesn't mean the off-the-shelf > ones can do as well.
frequently they are exactly the same drives, with exactly the same firmware.
you disable the write caches on the drives themselves, but you add a large write cache (with battery backup) in the raid card/chassis
> Are they SATA (or PATA) at all? SCSI etc. are usually different > animals, though there are SCSI and SATA models which differ only in > electronics.
it depends on what raid array you use, some use SATA, some use SAS/SCSI
David Lang
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