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

[Ric Wheeler]

On 09/03/2009 09:34 AM, 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.

Storage vendors have a wide range of options, but what you get today is a 
collection of s-ata (not much any more), sas or fc.

Some times they will have different firmware, other times it is the same.


> 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.
>
> Do you have battery-backed write-back RAID cache (which acknowledges
> flushes before the data is written out to disks)? PC can't do that.

We (red hat) have all kinds of different raid boxes...

ric


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