32GB here.

It all depends how long you want to wait to restore a file if you have 
large backups that can span a tape completely.

With 1TB fragment size, assuming there was no compression and you needed 
to restore a 10k file at the end of the tape, it would need to read the 
entire thing to restore the file.

If you used a smaller fragement size, it would skip to the closest 
fragment to the file that needed to be restored.

Don't go too small though or every time it writes a file marker, it could 
slow down the backup.

It is all about speed of backup vs. speed of restore (and the data type 
being backed up/restored) as well.

Justin.

On Wed, 16 Sep 2009, Dean wrote:

> 20GB here, using IBM 3592. I've considered making the fragment size larger,
> but ..... if it aint broke....
>
>
> On Wed, Sep 16, 2009 at 7:26 PM, <william.d.brown AT gsk DOT com> wrote:
>
>> 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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