Veritas-bu

[Veritas-bu] LTO3 throughput on Vault/Duplication jobs

2006-09-19 12:22:27
Subject: [Veritas-bu] LTO3 throughput on Vault/Duplication jobs
From: jonathan.marianu at cingular.com (Marianu, Jonathan)
Date: Tue, 19 Sep 2006 09:22:27 -0700
The use of any multiplexing has an adverse effect on duplication
throughput.

To maximize duplication performance either turn MPX Off or set it to a
high number (as much as 32).

Setting MPX to 1 (off) provides the best duplication performance and
restore performance but if there are not enough front end client facing
drives on the media server the backup streams will queue up behind slow
clients. 

If you can not turn MPX off, setting MPX to a high number provides
better throughput during duplication than a lower number because there
are more bptm processes reading from the tape. If it is set lower, like
8, only 8 processes can read from the tape; then the tape has to rewind
and then 8 more processes read, then it rewinds and it keeps doing this
until all images are finally duplicated. The tradeoff is that a higher
MPX setting means that a restore will take longer.

It is important to note that MPX is set during the creation of copy 1 of
the image.


Here is a method for visualizing vault duplication from VTL to tape on
Solaris.
I find this helps our new netbackup admins to understand duplication
better.

Start duplication
Identify the two PARENT bptm processes involved in the duplication.
In two separate windows run "truss -p" against each process id.
Place the window monitoring the reading bptm process on top of the
writing window.
Now you can see a visual representation of the images being read fromm
tape and written to tape.

__________________________________________
Jonathan Marianu (mah ree ah' nu)