On Wed, May 13, 2009 at 03:30:09PM -0400, George Sinclair wrote:
> Len Philpot wrote:
> >>George Sinclair 
> >>
> >>If you have a very large number of files on a given file system can this 
> >
> >>slow down the backup write speeds, not the actual completion times, but 
> >>the speed of the writing to tape itself?
> >
> 
> What if browsing was turned off? To do this, I'd have to set up a 
> separate tape pool. That's a pain and kind of silly for just one path, 
> but is doable. If browsing is turned off then NW has no metadata to 
> manage except that 1. it would still need to determine the fsize 
> beforehand for comparison after the backup for the given file completes 
> and 2. it still has a lot of open and close operations to perform. 
> That's not going to change. So, the next question would be which is a 
> more significant performance hit: the fact the browsing is enabled or 
> the fact that there's a lot of files to open and close, never mind the 
> fact the browsing were disabled?

I would expect a non-browseable backup to be similar in impact to
running 'tar cf /dev/null /filesystem'.  Tar is going to find, open, and
read every file.  When the files are tiny, that work dominates the job.
The fact that it's writing to a fast /dev/null instead of a limited
network pipe won't matter much.  So try that and see how long it takes.
If it's similar to your current backup time, then you won't see much
benefit.  If it's significantly faster, then it might be worthwhile.

Where it might matter is if you're getting middling tape speeds causing
some slowdown from the tape.  But it sounds like you're getting very
slow speeds that won't have this effect.

-- 
Darren

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