Tino Schwarze schrieb:
> On Tue, Jan 05, 2010 at 04:55:51PM -0500, John Drescher wrote:
> 
> > >> I'm not seeing anywhere close to 60M/s ( < 30 ).  I think I just fixed
> > >> that.  I increased the block size to 1M, and that seemed to really
> > >> increase the throughput, in the test I just did.  I will see tomorrow,
> > >> when it all runs.
> > >
> > > Yes, if you aren't already, whenever writing to tape you should almost
> > > without exception (and certainly on any modern tape drive) be using the
> > > largest block size that btape says your drive supports.
> > 
> > I tried to do that years ago but I believe this made all tapes that
> > were already written to unreadable (and I now have 80) so I gave this
> > up. With my 5+ year old dual processor Opteron 248 server I get 25MB/s
> > to 45MB/s despools (which measures the actual tape rate) for my LTO2
> > drives. The reason for the wide range seems to be compression.
> 
> Can anybody confirm or rebute this for 2.2.x? I'm currently fiddling
> with Maximum Block Size and a shiny new tape. It looks like 1M is too
> much for my tape drive, but 512K seems to work and it's making a huge
> difference: btape fill reports > 60 MB/s right at the beginning, then
> drops to abour 52 MB/s.

With

Maximum File Size = 5G
Maximum Block Size = 262144
Maximum Network Buffer Size = 262144

I get up to 150M MB/s while despooling to LTO-4 drives. Maximum File
Size gave me some extra MB/s, I think it's as important as the Maximum
Block Size.

Ralf

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