[Lustre-devel] storing SOM epoch in EA

[Eric Barton]

Rather than discussing this one EA at a time, should we not
consider any other EAs (e.g. being considered in current 
architecture work) that might contend for space in the inode?

> -----Original Message-----
> From: lustre-devel-bounces at lists.lustre.org 
> [mailto:lustre-devel-bounces at lists.lustre.org] On Behalf Of 
> Alex Zhuravlev
> Sent: 19 February 2008 9:49 AM
> To: lustre-devel at lists.lustre.org
> Subject: [Lustre-devel] storing SOM epoch in EA
> 
> 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
> again.
> 
> 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?
> 
> thanks, Alex
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