> I am doing some research to see if a VTL will help my NDMP performance. 
> 
> Currently I backup my Net App environment over the LAN. I am looking to 
> improve backup and restore performance. 
> 

> I have a LTO-3 Tape library that can be fiber attached to the Net App
> filer. My concern is that the Net App filer will not be able to stream
> to the tape drives and I will kill my performance since the tape will
> have to do lots of re-positioning and start and stop.

Possibly, possibly not.  I have a great number of direct attach LTO3
drives in use.  While shoeshining is an easy thing to point to and worry
about, I find it very difficult to test directly for understanding how
much of an impact it has.  In general, I've found that my filers under
load have bad peformance in all backup cases (even to a null device).

The big advantage of a VTL in such cases would be that you're not
binding a drive to a filer and making other backups wait for a drive.
Of course if you have sufficient drives that they're all directly
attached, there may not be a big win.

> I have newer and older Net App boxes, assuming a 2GB san, what
> performance can I expect using NDMP?

All over the board.  By default Netapp prefers to serve files over doing
system tasks (like NDMP).  A filer under heavy load can be brutal for
backup times.  I've seen one filer go from a 24 hour NDMP backup (to a
null device) to under an hour after we killed the load.  I don't
normally see anything above 80MB/s even to direct attach.

If you have 7.2 I think you can use FlexShare to change the priority
between user and system requests.  I've just now heard of the capability
and will be doing some testing in the future.

> Do you see an advantage using VTL in place of multiple LTO-3 drives?

If you're merging a small number of drives to many filers/streams, then
I think it would be an advantage.  Filers often take a long period of
time during incrementals where they are running the filesystem tree and
not sending data.  If this is a normal NDMP backup, then the drive is
allocated by NBU to the filer the entire time.  A VTL can make that
dramatically more efficient in incremental runs.  For fulls where the
Netapp is actually streaming data the whole time, it's probably less of
a win.

> How many streams are possible (Using NBU 6.x)? Do the number of
> streams help in a VTL environment? how about a tape environment?

One stream per NDMP target.  You can divvy up a volume into multiple
targets, but some of the NDMP overhead is shared on the volume.  You may
not get increased performance if you do that.  

Most of my backups are one stream per volume.  I have a problem volume
that is huge that I use multiple streams on to keep the size of the
individual images lower.

> Any recommendations on performance tuning with NBU 6 and NDMP?

Not many.  Most of the performance is on the NDMP side.  NBU can slow
things down if you're doing a lot of backups (especially small files)
and the history data going to the catalog has to wait for the NBU master
to write the catalog.  Speeding up the master could help then.  

Overloaded filers (near 100% cpu) do slow backups.

-- 
Darren Dunham                                           ddunham AT taos DOT com
Senior Technical Consultant         TAOS            http://www.taos.com/
Got some Dr Pepper?                           San Francisco, CA bay area
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