I'm using a 10G fragment size.  Just a guess at a ballpark figure
between too small & too large.

-M

-----Original Message-----
From: veritas-bu-bounces AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of
william.d.brown AT gsk DOT com
Sent: Wednesday, September 16, 2009 3:26 AM
To: veritas-bu AT mailman.eng.auburn DOT edu
Subject: [Veritas-bu] Fragment size for LTO4 on NBU 6.x

What are people using for the fragment size on LTO4 (or I guess LTO3)
with 
NBU 6.x?

I ask because the default is 1TB, i.e. more or less don't fragment.

The argument for a large fragment is that the backup doesn't have to
stop 
so often as it does briefly at the end of each fragment to update the 
Master, and also the inter-fragment file markers waste space..though 
that's hardly a consideration on such large tapes now.

The argument for a small fragment was that the tape can position at full

speed to the file marker for the appropriate fragment for a restore, 
rather than reading the tar file from the top at read speed, which for a

large tape could be a very long time.

We used to (dating back to DLT7000) set a 2GB fragment, as back then
this 
was thought a good idea in case you wanted to dd the tape to disk and
read 
it without NetBackup.  UNIX file systems did not take files > 2GB.  Well
I 
can't say we ever tried it and it's a silly small size now.

But what are people using - 100GB?  200GB?  Does it really make a 
difference...

William D L Brown


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