On Tue, Sep 18, 2012 at 1:18 PM, Timothy J Massey <tmassey AT obscorp DOT com>
wrote:
>
> That is a good point, but if I ever have to do a full 3TB restore from
> BackupPC, the 12 hours a (properly performing) BackupPC will take is not my
> biggest issue. I don't look at BackupPC as my bare-metal disaster recovery
> plan--or, at least, not my first line of such defense. That's what
> snapshots and virtualization provides. BackupPC is for file-level restores,
> and the odds of having to do a full restore from BackupPC is small.
Off topic, but if you haven't already, have a look at ReaR for linux
bare-metal restores. There is some active development in progress.
It builds a bootable iso with the system's native tools and includes
scripts to reconstruct the filesystems. It wouldn't be too hard to
make it accept a backuppc restore directly in addition to the options
it already handles. It might be even nicer if instead of building
the iso it just made a directory of the contents that backuppc could
include and pool nicely. Then you'd start the restore by downloading
that and burning a current iso.
> Unfortunately, both of these boxes are in production, so they can't be
> reconfigured; and I don't have enough parts for another one just yet. It
> is something worth trying. I predict that this won't make that much of a
> difference: I've tested small-write performance differences between
> single-disk, RAID 1, RAID 10 and RAID 5 (but not RAID 6) before, and the
> penalties, while very real, were also very manageable.
>
> But I'll see if I can try it again.
I'm not convinced that benchmarks replicate backuppc activity very
well. It seems more likely to have the small writes splattered
randomly over the disk than a test run creating new files and aside
from the extra seeking it is likely to have your disk buffers full of
stuff that isn't what you want next. If you have spare RAM around
could you try cramming a lot more in to see how much it helps?
> > Not sure, but I am sure that raid5/6 is a bad fit for backuppc
> > although good for capacity.
>
> And frankly, capacity is what I need more, with a certain minimum amount
> of performance. I do not need top-performance, and am perfectly willing to
> sacrifice performance for capacity, as long as I could get, say, 50MB/s of
> BackupPC throughput.
Yes, but raw disk space isn't that expensive anymore - just the real
estate to park them...
> > Are you sure the target has no
> > other activity happening during the backup?
>
> I am sure they *are* seeing other activity: they're file servers, mail
> server, etc. But their loads are all very low across the board.
I always think 'seek time' whenever there is enough delay to notice -
and anything that concurrently wants the disk head somewhere else is
going to kill the throughput.
--
Les Mikesell
lesmikesell AT gmail DOT com
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