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

From: Ric Wheeler
Date: Thu Sep 03 2009 - 09:52:01 EST

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

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

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...


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