[OpenAFS] Overview? Linux filesystem choices

[Stephan Wiesand]

--Apple-Mail-322-451830359
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=us-ascii

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


--Apple-Mail-322-451830359
Content-Disposition: attachment;
	filename=smime.p7s
Content-Type: application/pkcs7-signature;
	name=smime.p7s
Content-Transfer-Encoding: base64
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--Apple-Mail-322-451830359--