[Veritas-bu] Fragment Sizes...

David Rock dave-bu at graniteweb.com
Mon Mar 7 12:52:56 CST 2005


* william.d.brown at gsk.com <william.d.brown at gsk.com> [2005-03-07 16:27]:
> 
> However a significant counter-argument, which many sites will find 
> persuasive, is that the restore speed is also affected by the fragment 
> size.  In the extreme case, that you don't have a fragment size set at 
> all, there is just one fragment on a tape.  Any restore has to scan (at 
> slow speed) the whole tape, reading it until the files required for 
> restore are found.   With fragments, the tape can skip forward at high 
> speed to the required fragment (it is just a record to the tape); it then 
> has to read just that fragment at slow speed to get the files.  So unless 
> you files are themselves >2GB, you would likely be happy with the 2GB 
> fragment size.  It really depends on your data, and how often you do 
> restores, how quick they have to be...vs some improved write speed.

We have ours set to 2G for exactly this reason. we often have very large
backups >500G with restore requests that would take forever without
giving NBU a hint where to look for it.

-- 
David Rock
david at graniteweb.com
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