Les Mikesell <email@example.com> wrote on 09/18/2012
> On Tue, Sep 18, 2012 at 10:24 AM, Timothy J Massey
> <firstname.lastname@example.org> 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
> 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
> 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
But I'll see if I can try it again.
> > Might it have something to do with md? Could the time that
> > be considered wait time for BackupPC be counted as CPU time for
> > doesn't seem logical to me, but I can say that there just isn't
> > 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.