On Tue, 10 Mar 2009 18:05:52 -0000, "Synapse Syndrome"
wrote:
Jaimie Vandenbergh wrote:

Also,
JBOD (also "not a RAID", Just a Bunch of Disks): N disks of any sizes,
gives the combined sum of diskspace as one virtual disk with no
safety.

I've never seen the point of JBOD. Do people actually use it?

I've been using one for a couple of years now.

If one drive
fails, you lose everything (without having to go through a recovery
process - and what happens to files that span different physical drives?)

It's not striped, so you'll lose everything from the failed drive
forward - how fatal that is depends on which disk pops and how
resilient your filesystem is.

and there is no advantage as far as I can see. It would be much better to
extend a drive using volume mount points or symbolic links, no?

Here's my use case: I've got a NAS box with 3x1Tb in, RAID5 so 2Tb
disk space. I like to back it up, because RAID isn't backup of course.

So it's backed up nightly to a 2Tb JBOD. The 4x500gig that used to be
in the NAS are now in a four bay USB enclosure (Edgestor DAS400) that
has a "JBOD" switch on the back.

Nice and simple, completely transparent to the host (which is the NAS,
so it needs to be transparent), and without any risk of individual
folder trees running short of space. And if a disk pops, who cares?
The original is still RAID5 protected, so bang in a fresh disk,
resync, done.


I'd never recommend them for anything else except second or later
level backups, obviously.

(previously, when the 4x500gig RAID5 = 1.5Tb were in the NAS, I backed
that up to a 4x320gig JBOD that was the original content of the NAS -
recycling at work! I upgraded when the JBOD ran out of space)

Cheers - Jaimie
--
If it's worth doing, it's worth overdoing.