> Message: 9
> Date: Tue, 03 Jul 2007 08:18:23 -0700
> From: Kenny <netbackup-forum AT backupcentral DOT com>
> Subject: [Veritas-bu] VTL with NDMP
> To: VERITAS-BU AT mailman.eng.auburn DOT edu
> Message-ID: <1183475903.m2f.173807 AT www.backupcentral DOT com>
>
>
> 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.
So you are running three-way NDMP right now? Or are you backing up over NFS?
> 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.
>
> I was thinking a VTL would be able to match the speed of the net app box
> thus the performance would be optimized.
LTO-3: 80 MB/s native, 160MB/s compressed. That's pretty fast.
VTL: 100-180 MB/s. Make sure your VTL vendor is doing compression in
hardware, otherwise turning on compression can reduce your speeds by
50%.
We have a very large NDMP (EMC Celerra -> LTO-3) shop here, and I can
tell you that very rarely does the backend disk have the horsepower to
push LTO-3 much faster than 95 MB/s with real-world tests. With
contrived data on a stand-alone Celerra we saw less than a 5%
difference between LTO-3 and the VTLs that we were testing. YMMV, of
course, but we didn't see a large enough performance advantage to move
to VTL. Not only that, but if you are backing up data with long
retention periods, be prepared to buy a whole lot of disk for your
VTL, unless you will archive off to tape from your VTL.
> Questions:
>
> I have newer and older Net App boxes, assuming a 2GB san, what performance
> can I expect using NDMP?
>
Out of the box, untuned, 50-80 MB/s to LTO-3. Tuned, 70-160 MB/s.
>>From my experience, VTLs don't really need much tuning, as does tape.
They are fast out of the box, but tape can be almost as fast (within
5%) when tuned properly.
> Do you see an advantage using VTL in place of multiple LTO-3 drives?
Depends on your data. If you are backing up mostly data that is
already compressed, you will be limited to the native speed of LTO-3,
which is 80 MB/s. A VTL will be faster in that case. However, if
your data is mostly uncompressed, then tape is just as fast as VTL.
Also, if you have 2 Gb/s coming out of your NetApp, and 2 Gb/s coming
into your VTL, the most you are going to see is 240 MB/s. That's
three LTO-3 drives. Sure, you can create 16 virtual drives on your
VTL, but that's 500% oversubscribed on throughput.
>
> How many streams are possible (Using NBU 6.x)? Do the number of streams help
> in a VTL environment? how about a tape environment?
A NetApp filer supports 16 concurrent NDMP sessions at one time. They
cannot be muxed, but you can certainly multi-stream to individual
drives concurrently.
>
> Any recommendations on performance tuning with NBU 6 and NDMP?
This is more of an issue with tape than VTL. With tape,
SIZE_DATA_BUFFERS_NDMP is your friend.
HTH.
-- nick
>
> Thanks in advance!
>
> Paul Kenny
>
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