[Discuss] lvm snapshot cloning

[dsr at tao.merseine.nu (Dan Ritter)]

On Tue, Oct 25, 2011 at 11:20:40PM -0400, markw at mohawksoft.com wrote:
> >
> > Data point: It takes ~19 hours to restore 7.5TB from enterprise-class
> > Tivoli Storage Manager over 1GB Ethernet to a 12x1TB SATA (3Gb/s) RAID 6
> > volume.  I had to do it this past spring after the RAID controller on that
> > volume went stupid and corrupted the whole thing.
> 
> Yes, and it should be MUCH faster!!! I agree.


The bottleneck there is the the gigabit ethernet:

1000Mb/s * 3600s/h * B/8b = 450000 MB/h or 450 GB/h. 
7500/450 = 16.7 hours

So the absolute best you could have done ignoring all overhead was 16.7
hours, and it took 19. Not awful.

On the other hand, going to 10GE doesn't move the bottleneck to
the disks -- if you can get 160MB/s per spindle and 10 of the 12
spindles effective, that's:

1600MB/s * 3600s/h = 5760GB/h which is still more than the
4500GB/h you might get from theoretical no-overhead 10GE.

Assume 10GE with the same 87% efficiency as GE and you get 3.9TB/h,
or about two hours to do your 7.5TB restore. OK, so 10GE is a win for
time, no surprise. However, GE is essentially free (your motherboards
have it, your switching infrastructure is in place) but 10GE involves
$600/port upgrades to the NIC (if you have room) and $1000/port switch
upgrades. Good thing to have next time around, probably not a routine
upgrade for most operations.

-dsr-

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