[Lustre-devel] Wide striping

Nathan Rutman Nathan_Rutman at xyratex.com
Tue Oct 4 10:44:34 PDT 2011

On Oct 3, 2011, at 5:17 PM, David Dillow wrote:

> On Mon, 2011-10-03 at 13:15 -0700, Nathan Rutman wrote:
>> Some OST’s may be down at file creation time, or new OSTs added later;
>> hence there will likely be holes in the bitmap (but relatively few).
>> Start index will still be used, but stripe order will be strictly
>> round-robin (we will wrap around).  In other words, the stripe
>> sequence will always be in linear OST order, starting from
>> start_index, maybe skipping some holes, wrapping around to
>> start_index-1.
> It didn't occur to me when spoke at EOFS, but you'd need to store the
> number of OSTs in the system when the mapping was created if you allow
> it to wrap around -- otherwise, adding OSTs later would cause existing
> files to loose track of the objects after the wrap point.

That's done inherently in the bitmap, where everything beyond the current number of OSTs is marked as a hole.
(So actually, there will typically be one giant hole at the end of every bitmap, and then maybe some singeltons for deactivated

> -- 
> Dave Dillow
> National Center for Computational Science
> Oak Ridge National Laboratory
> (865) 241-6602 office
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