On Tue, 2007-01-09 at 17:31 -0800, Sridharan Ramaswamy (srramasw) wrote:

Sridharan,

> Yeah, I know you can have OST on top of an LVM-based logical-volumn.
> But my understanding (from a previous mail in this alias) is OST can't
> reflect the size change of the underlying logical volumn it is based
> on. 

Right.

> In plain words, if I do a lvextend or lvreduce on that logical-volumn,
> Lustre won't pick the OST size change and hence it won't reflect in
> the size change in the filesystem that OST is participating in. Is
> this understanding correct?

This is correct, because on top of the logical volume is an ldiskfs
(ext3 with a few patches) filesystem and it's in that filesystem that
the lustre OST does it's work -- stores objects and so forth.

So as I am sure you know with a regular ext3 filesystem, simply
expanding the LV it's on won't reflect a change in the filesystem's size
without first growing the filesystem.  This is why an OST doesn't see an
LV-only growth as making more space available.  That ldiskfs (ext3)
filesystem sitting between lustre and the LV needs to grow too.  That is
what Peter was referring to in his follow up message in this thread
about dynamic resizing.

Cheers,
b.


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