Ideally, I try to go for FAST restores. I feel our backups are quite
quick.
We also use buffer settings on some Media Servers that contains large
amounts of Data.

I guess it is a weigh up between performance and fast restores.

Simon 

-----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 Justin
Piszcz
Sent: Wednesday, September 16, 2009 2:13 PM
To: Dean
Cc: veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] Fragment size for LTO4 on NBU 6.x

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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