[Lustre-devel] New Pools DLD

[Andreas Dilger <adilger@sun.com>]

On Feb 27, 2008  14:50 +0300, Nikita Danilov wrote:
> Andreas Dilger writes:
> > are you aware of any desirable LOV EA changes that would be good to
> > include with the changes for the v3 "pool" EA (attached)?  Are there
> > any changes that are desirable for e.g. FIDs or similar?
> 
> I think that if we are introducing incompatible LOV EA format, we can as
> well go forward with changes hinted to at
> 
> http://arch.lustre.org/index.php?title=MDS_striping_format#Future_developments

Nikita, sorry to take a long time to get back to this issue, but I think
it is quite valuable to pursue if we are already going to change the
on-disk format.

Since we are already need to change the LOV_MAGIC value, we may as well
do as you suggest and have 0x0BD3ssss instead of 0x0BD30BD0, where
ssss = size of EA in bytes.

That would limit us to a 65536-byte striping EA, but it still larger than
what is supported today, and the plans for wide striping also do not call
for larger EAs.  Even supporting 64kB EAs  would be an issue with the
current nifrastructure because the client always has to preallocate a
receive buffer large enough for the largest EA because it does not know
the EA size in advance.

The question is whether you think we should also add a magic + size to the
lov_ost_data_v1 structure, which is currently the same for all EA types.
Adding a per-stripe magic + size would reduce the number of stripes we
can allocate per file, and the 160-stripe limit is already a problem for
some systems with more than 160 OSTs.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.