Re: Max obtainable performance for a single OST

On Fri, 2007-13-04 at 17:30 +0200, Andrei Maslennikov wrote:
> Performance of a single OSS depends on the perfomance of the local
> ext3 backend
> file system, and we were unable to push it over 750 MB/sec.

Nomenclature in such a discussion is very important.  An OSS is an
Object Storage Server.  An OSS can contain many OSTs.  An OST is an
Object Storage Target.  An OST is a Lustre building block constructed
from a single block device, be it a single physical disk (/dev/sda for
example) or a partition on a disk (/dev/sda1 for example) or an LVM LV
(/dev/vg00/ost1 for example), or a software raid device (/dev/md0 for
example) or the block device a hardware RAID card presents to the
operating system.

> The advice of Andreas 
> from Clusterfs is to use 3 OSTs inside one OSS and stripe files over
> all three of them.

Right.  I believe the 3 OSTs he recommended you use would be the three
RAID disks you have in the machine.

> Time ago we have however considered and discarded this solution as we
> wanted  
> to ensure that every file is confined to one and only one OSS capable
> to deliver 
> 0.9-1 GB/sec.

Do you really mean OSS here or OST?  Given the 3 OSTs you would put on
the 3 RAID cards you have in your OSS, this would meet your requirements
wouldn't it?

> Setting the filesystem default stripe count to 3 may lead to a
> situation 
> when a file may end up on different OSS machines,

I believe Andreas described striping across the 3 OSTs in that single
OSS machine.

> and that's exactly what we want 
> to avoid. (I have asked Andreas to comment on the configuration; would
> it be possible 
> to migrate to striping over 3 OST per OSS, and still ensure the OSS
> confinement,

Sure.  I do think that is what Andreas was suggesting.

b.