Les Mikesell <lesmikes...@gmail.com> wrote on 09/18/2012 12:42:26 PM:
> On Tue, Sep 18, 2012 at 10:24 AM, Timothy J Massey
> <tmas...@obscorp.com> wrote:
> >
> > Fortunately, BackupPC is a "backup of the backup" right now, and is
not
> > expected to be used for real. Yet. That's why I can take the time
and try
> > to actually solve the problem, rather than apply band-aids.
> >
> > But that will likely end in November, if not sooner.
>
> It is more than a band-aid to have a warm-spare disk ready to pop in
> instead of waiting for a 3TB restore even with reasonable performance.
> Be sure everyone knows what they are losing.
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.
> > I'm not. I've got two of these new boxes built. In both cases, they
have
> > 2-4% wait time when doing a backup. One is a RAID-5 and one is a
RAID-6.
>
> Can you test one as RAID10? Or something that doesn't make the disks
> wait for each other and likely count the time against the CPU?
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.
> > Might it have something to do with md? Could the time that would
normally
> > be considered wait time for BackupPC be counted as CPU time for md?
That
> > doesn't seem logical to me, but I can say that there just isn't any
wait
> > time on these systems.
>
> 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.
50MB/s performance for a RAID-5/6 array should not be difficult, even with
read/modify/write and small transactions. I thought I had tested this
workload on this array successfully, giving me more like 80-100MB/s on
synthetic benchmarks.
But again, I'll see what testing I can do.
> 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.
Timothy J. Massey
Out of the Box Solutions, Inc.
Creative IT Solutions Made Simple!
http://www.OutOfTheBoxSolutions.com
tmas...@obscorp.com
22108 Harper Ave.
St. Clair Shores, MI 48080
Office: (800)750-4OBS (4627)
Cell: (586)945-8796
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