[OpenAFS] Tuning openafs write speed

[Hartmut Reuter]

Kai Moritz wrote:
> Hi folks!
> 
> I would like to try tuning the speed of my openafs installation, but
> the only information I could google is this rather old thread 
> (http://www.openafs.org/pipermail/openafs-info/2003-June/009753.html)
> and the hint to use a big cache-partition.
> 
> For comparison I've created files with random data and different size
> (1MB, 2MB, 4MB, 8MB, 16MB, 32MB, 64MB and 128MB) on my local disk. I
> copied them into AFS and then I copied then to the same disk on the
> same host via scp (without compression). I've done that 10 times and
> computed the average. For the 1MB file AFS ist slightly faster then
> scp (factor 0,89). For the 2 and the 4MB file AFS needs about 1,4 of
> the time scp needs. For the 8, 16 and 32MB the factor is about 2,7
> and for the 64 and the 128MB file it is about 3,3.
> 
> I've already tried bigger cache-partitions, but it does not make a
> difference. Are there tuning parameters, which tell the system a
> threshold for the size of files, beyond which data won't be written
> to the cache?
> 
> Greetings Kai Moritz

What are your data rates in MB/s?
If you are on a fast network (Gbit Ethernet, Inifiband ...) a disk cache
may be remarkably slower than the network. In this case memory cache can 
help.

Another point is chunk size. The default (64 KB) is bad for reading 
where each chunk is fetched in a separate RPC. with disk cache bigger 
chunks (1 MB) can be recommanded, anyway. For memory cache of, say, 64 
MB you would limit the number of chunks to only 64 which is certainly 
too low.

Here ramdisks can help because many of the chunks are filled with short 
contents, such as directories and symbolic links. The additional 
overhead to go through the filesystem layer may be less than what you 
can earn from bigger chunks. With ramdisk 1 MB chunks aren't too bad.

Hartmut

-- 
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Hartmut Reuter                           e-mail reuter@rzg.mpg.de
					   phone +49-89-3299-1328
RZG (Rechenzentrum Garching)               fax   +49-89-3299-1301
Computing Center of the Max-Planck-Gesellschaft (MPG) and the
Institut fuer Plasmaphysik (IPP)
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