Re: raid is dangerous but that's secret (was Re: [patch] ext2/3:document conditions when reliable operation is possible)

[david]

On Thu, 3 Sep 2009, Krzysztof Halasa wrote:

> Ric Wheeler <rwheeler@xxxxxxxxxx> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/