On Tue, 26 Jul 2011 06:18:25 -0700
Steve Ellis <ellis AT brouhaha DOT com> wrote:

> >> Another point, even with your current config, if you
> >> aren't doing data spooling you are probably slowing things down
> >> further, as well as wearing out both the tapes and heads on the
> >> drive with lots of shoeshining.
> > (I'm asking as a person having almost zero prior experience with
> > tape drives for backup purposes.)
> >
> > Among other things, I'm doing full backups of a set of machines to a
> > single tape--yes, full backup each time, no incremental/differential
> > which means I supposedly have just straightforward data flows from
> > FDs to the SD.  At present time I have max concurrent jobs set to 1
> > on my tape drive resource and no data spooling turned on.
> > Would I benefit from enabling data spooling in this scenario?
[...]
> OK, perhaps I'm not the best person to ask, but here's what I do know:
> 
> Even with only 1 job at a time, if you aren't able to deliver data to 
> the drive at its minimum streaming data rate (for LTO4, probably at 
> least 40MB/sec--possibly varies by manufacturer), then the tape 
> mechanism will have to stop, go back a bit, wait for more data, then 
> start up again--all of this takes time, and increases wear on the
> tapes and drive heads.
[...]
> I hope this helps,

Apart from giving me the knowledge of this mechanics, your message
made me sit down and make some measures.  So I discovered that my LTO-4
drive is actually faster to write (up to 10 times) than my local
filesystems are to read (and I was absolutely sure it's the other way
round).  We're now considering implementing a raid0 for data spooling.
Hence, thanks!

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