[OpenAFS] Overview? Linux filesystem choices

Stephan Wiesand stephan.wiesand@desy.de
Thu, 30 Sep 2010 14:19:51 +0200


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Hi Jeff,

On Sep 29, 2010, at 22:18 , Jeffrey Altman wrote:

> RAID is not a replacement for ZFS.  ZRAID-3 protects against single =
bit
> disk corruption errors that RAID cannot.  Only ZFS stores a checksum =
of
> the data as part of each block and verifies it before delivering the
> data to the application.  If the checksum fails and there are =
replicas,
> ZFS will read the data from another copy and fixup the damaged =
version.
> That is what makes ZFS so special and so valuable.  If you have data
> that must be correct, you want ZFS.


you're right, of course. This is a very desirable feature, and the main =
reason why I'd love to see ZFS become available on linux.

I disagree on the "RAID cannot provide this" statement though. RAID-5 =
has the data to detect single bit corruption, and RAID-6 even has the =
data to correct it. Alas, verifying/correcting data upon read is not a =
common feature. I know of just one vendor (DDN) actually providing it. =
It's a mystery to me why the others don't.

Anyway, the next best option if ZFS is not available is to run parity =
checks on all your arrays regularly. Things do get awkward when errors =
show up, but at least you know. Both Linux MD RAID and the better =
hardware solutions offer this.

=46rom my experience, disks don't do this at random and do not develop =
such a fault during their life span, but some broken disks do it =
frequently from the beginning. NB I only ever observed this problem with =
SATA drives.

Best regards,
	Stephan=20

--=20
Stephan Wiesand
DESY -DV-
Platanenenallee 6
15738 Zeuthen, Germany


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