James Overman HP Support Technology Lab  Roseville, CA asks:

If you would be so kind to provide some specifics for those of us who
have to consider methods of backing up larger and larger systems:

Q.  What kind of DDS drives are you using?  90M dds-1 or 120M dds-2?
A.   We are using 120M dds-2
Q.  How long does it take per tape set (assumes multiple tapes per drive)
  and total clock time?
A.  It currently takes 3 hours with 4 tape drives/4 tapes.  Sometimes we
go to 5 or 6 drives and you must account for operator time.

Q. Hardware or software compression?
A.  We use software compression see the next answer

Q. Which backup software package and important options?
Online or with users offline?
A.  We use Roadrunner with Online feature and more importantly parallel
threads.

Q. What are your typical CPU and IO Rates? Do you really expect a linear
performance/elapsed time from 4 to 11 tape drives?
A.  Each thread will use up as much CPU as it needs, with four threads our
CPU's are being fully utilized.  As I understand it,   Roadrunner is
typically bound by the  IO channels that you have available.

Q.  Finally, what are your disc types/sizes/number.
A.  We have 196 Gbytes mirrored on 2GByte drives plus the system disks
that use Raid.

In discussion with the vendor, I do expect a great performance boost.
Their reccommendation is that they can handle 2 DAT's per SCSI channel.
If you put more on a SCSI channel, then your channel becomes a bottleneck.
 Even though, we have online, I fully expect 11 Roadrunner threads to
totally dominate the CPU's, channels, etc.  But by throwing the hardware
at it, we also feel we can get the shortest backup time.  Our original
goal was 2 hours with some online work.  However, our software requires
database reindexing that takes about 45 minutes with our current online
backup running.  Also some batch jobs start up after the indexing is
complete.

When I took this assignment as a consultant, the original backup solution
was 3480 tapes.  I asked how many would we need a night.  The answer was
150 tapes per night, but they are fast.  That's when we started looking at
other solutions.  We figured that our operators would need additional
training with inline roller skates just to keep up with the tape activity.
  DLT's was our second choice.  We determined for optimal performance that
1 DLT/SCSI channel would be needed.  We estimated 5 DLT's would be about
right.  Unfortunately, DLT's are not supported by HP.

Terry Warns
WL Software