[Lustre-discuss] Optimal stratgy for OST distribution

[Kevin Van Maren]

It used to be that multi-stripe files were created with sequential OST 
indexes.  It also used to be that OST indexes were sequentially assigned 
to newly-created files.
As Lustre now adds greater randomization, the strategy for assigning 
OSTs to OSS nodes (and storage hardware, which often limits the 
aggregate performance of multiple OSTs) is less important.

While I have normally gone with "a", "b" can make it easier to remember 
where OSTs are located, and also keep a uniform convention if the 
storage system is later grown.

Kevin


Heckes, Frank wrote:
> Hi all,
>
> sorry if this question has been answered before.
>
> What is the optimal 'strategy' assigning OSTs to OSS nodes:
>
> -a- Assign OST via round-robin to the OSS
> -b- Assign in consecutive order (as long as the backend storage provides
>     enought capacity for iops and bandwidth)
> -c- Something 'in-between' the 'extremes' of -a- and -b-
>
> E.g.:
>
> -a-     OSS_1           OSS_2           OST_3
>           |_              |_              |_
>             OST_1           OST_2           OST_3
>             OST_4           OST_5           OST_6
>             OST_7           OST_8           OST_9
>
> -b-     OSS_1           OSS_2           OST_3
>           |_              |_              |_
>             OST_1           OST_4           OST_7
>             OST_2           OST_5           OST_8
>             OST_3           OST_6           OST_9
>
> I thought -a- would be best for task-local (each task write to own
> file) and single file (all task write to single file) I/O since its like
> a raid-0 approach used disk I/O (and SUN create our first FS this way).
> Does someone made any systematic investigations which approach is best
> or have some educated opinion?
> Many thanks in advance.
> BR
>
> -Frank Heckes
>
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