>> On Thu, 12 Jul 2007 07:32:27 -0500, Andy Huebner <Andy.Huebner AT ALCONLABS 
>> DOT COM> said:

> To me it is not the incoming, but the outgoing that is the greatest
> concern.  If the next pool is physical tape, be sure you have enough
> speed to keep up with your tape drives.  If the disks cannot keep up
> with the physical tape drives then performance will not be acceptable.
> Since many VTLs use ATA disks we know it can be done.


This is a really good point.  Keeping the number of read streams under
control will make a huge difference in your performance.

When I drain a SATA pool with a single thread, I can drive one of my
3592s at 80-90 MB/s.  When I put three of them on the job, aggregate
throughput drops to ~30 MB/s (yes, each drive getting ~10MB/s).

- Allen S. Rout