[lustre-discuss] Stripe size for osts

[Dilger, Andreas]

On 2016/03/18, 12:52, "Kurt Strosahl" <strosahl at jlab.org> wrote:
>Good Afternoon,
>
>    I'm experimenting with ost configurations geared more towards small
>files and operations on those small files (like source code, and
>compiling), and I was wondering about changing the stripe size so that
>small files fit more efficiently on an ost.  I believe that would be the
>--param lov.stripesize=XX option for mkfs.lustre, is that correct?  And
>is there a lower limit that I should know about?

Just to clarify, the stripe size for Lustre is not a property of the OST,
but rather a property of each file.  The OST itself allocates space
internally as it sees fit.  For ldiskfs space allocation is done in units
of 4KB blocks managed in extents, while ZFS has variable block sizes (512
bytes up to 1MB or more, but only one block size per file) managed in a
tree.  In both cases, if a file is sparse then no blocks are allocated for
the holes in the file.

As for the minimum stripe size, this is 64KB, since it isn't possible to
have a stripe size below the PAGE_SIZE on the client, and some
architectures (e.g. IA64, PowerPC, Alpha) allowed 64KB PAGE_SIZE.

For small files, the stripe_size parameter is virtually meaningless, since
the data will never exceed a single stripe in size.  What is much more
important is to use a stripe_count=1, so that the client doesn't have to
query multiple OSTs to determine the file size, timestamps, and other
attributes.

Cheers, Andreas
-- 
Andreas Dilger

Lustre Principal Architect
Intel High Performance Data Division