[Lustre-devel] storing SOM epoch in EA
Yury.Umanets at Sun.COM
Tue Feb 19 02:28:15 PST 2008
Alex Zhuravlev wrote:
> Good day,
> some time ago we discussed that it would be very helpful to
> store epoch in inode on mds. the perfect solution could be
> to store epoch in old inode body, but there is no much space
> for this in the body and with DMU we'll have this problem
> given the minimal inode size we use on MDS is 512 bytes, we
> can store upto 13 stripes in the body. larger EAs go to a
> dedicated block. if we add 8 byte epoch, then we can store
> upto 12 stripes in the body. so, epoch stored in EA affects
> only files with exactly 13 stripes. files with different
> stripes are unaffected at all.
> couple lesser concerns are:
> 1) cpu usage
> 2) epoch on old filesystem with insufficient inode space
> any objections to use EA to store SOM epoch?
Can we use IAM for storing epoch? It is fast and does not have such
strong size limitations. We could make "epoch" index in mkfs time (like
it is done for existing indexes now) and use object's fid as a key and
epoch as value.
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