John Drescher <drescherjm AT gmail DOT com> wrote:
> I believe it is much better for your backups to use individual disks.
Why ? Single disk means a single failure leads to data loss. So it's not
reliable by itself. RAID is far from perfect, but RAID1 and RAID6 have
good price/size/reliability trade-offs, one can usually find something
right for one's use. I just loss a drive in a RAID6 for a Lustre
failsystem this morning, and nobody but the sysadmins noticed. It's
rebuilding the disk as I write. There's still some parity in case
another drive fails before the rebuild is done.
I would't use RAID5 anymore now that we have cheap RAID6, in particular
for large SATA arrays (rebuild time is way too long), but it's still a
lot more reliable than a LVM spanning the same number of disks. Using
your JBOD are multiple storage units means a lot more work, even if you
do gain than a failure means only a fraction of the data is gone.
Redudancy is key. RAID1 gives you 200% ; RAID5 or RAID6 will give you
1xy%, where xy depends on the number of disks in the array. Single disk
are 100%, redundancy must come from somewhere else.
The only way to get redundancy is to copy your backups to multiple
single disks. Which if done the trivial way will basically be RAID1 w/o
the simplicity. If you actually interlace the data it's a little bit
better because you limit the amount of data lost to a failure, but it's
a lot more complicated to implement.
I may be missing something, but unless you make multiple copies of datas
that each easily fit in less than one disk, I fail to see how this is an
improvement. And for me, the administration headaches aren't worth the
hassle. If you have a good explanation for your belief, I always like to
learn :-)
My bacula setup is to merge all my data from the various servers (all
use RAID :-) to a large RAID6 array of SATA drives, with hot spare,
holding full/differential/incremental. Because that's far from 100%
safe, we also have weekly full on off-site LTO-4 tapes, just in case.
Really critical data (CVS & SVN) have extra copies on other RAID arrays
and regular dump-to-DVDs, just in case (that's what fireproof safe are
for, after all).
Cordially,
--
Romain Dolbeau
<romain AT dolbeau DOT org>
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