[lustre-discuss] Real cases where setstripe is useful

[Mohr Jr, Richard Frank (Rick Mohr)]

> On Mar 15, 2016, at 7:42 AM, Patrick Farrell <paf at cray.com> wrote:
> 
> By default, file creation is round robin-ed across OSTs (and the default stripe count is one).  You can change this in various ways, but that's the standard setup.

That is true until the OST usage starts to become imbalanced, at which point Lustre will start allocating using the QOS method.  The default tipping point for Lustre is 17%  (based off the value in /proc/fs/lustre/lod/<fsname>-MDT0000-mdtlov/qos_threshold_rr from a recent Lustre install).  Although I think that some products (like the Sonexion) ship with this value set to 100% which forces round-robin allocation all the time.

--
Rick Mohr
Senior HPC System Administrator
National Institute for Computational Sciences
http://www.nics.tennessee.edu