On 11-Feb-09, at 10:08 AM, David Dyer-Bennet wrote:
On Tue, February 10, 2009 23:43, Uwe Dippel wrote:
1. Can the relevant people confirm that drives might turn dead when
leaving a pool at unfortunate moments? Despite of complete physical
integrity? [I'd really appreciate an answer here, because this is
what I
am starting to implement here: ZFS on USB drives.]
2. Are those drives in unrecoverable state passing their
integrity/diagnosis tests (r/w)?
3. If what has been mentioned, that a pool is an entity like RAID in
between and hurting the pool might as well destruct data, if this
is the
case, can this destruction of a pool not also happen within the
confines
of a server, without any physical yanking of the drive, by a dying
controller?
Seems like a power failure, controller failure, or processor
failure could
all produce the equivalent of yanking a USB cable. As could a cat
knocking an external drive off the desk :-). All of those things are
real-world issues that we must contend with.
And journaled/transactional systems are designed to deal with that
just fine.
The exception was clearly noted by Jeff.
The two hardware failures
are entirely possible even in a top-end commercial machine-room
installation. (For that matter, the power failure is, too; I've seen
places where the UPS came on fine when the power failed, and the
generator
cut in fine before the UPS failed...and then the automatic fail-BACK
failed, and everything went dark when the generator ran out of fuel).
Yes, this happens in *every* data centre eventually. Data centres are
also subject to many of the usual human errors.
--Toby
I confess to not being adequately reassured right now that my
external USB
backup disks are reasonably secure.
This all-or-nothing behavior of ZFS pools is kinda scary. Turns
out I'd
rather have 99% of my data than 0% -- who knew? :-) I'd much
rather have
100.00% than either of course, and I'm running ZFS with mirroring, and
doing regular backups, because of that.
--
David Dyer-Bennet, d...@dd-b.net; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info
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