[lustre-discuss] Overstriping setting

[Wei-Keng Liao]

When setting the overstriping for a new file, is it possible to let
the MDS to choose the OST indices?

I was able to use lfs command to set an overstiping for a new file.
For example, to overstripe a file over 4 OSTs with 2 stripe per OST,
I am using this command:

%  lfs setstripe -c 4 -C 8 -o 10-13,10-13 $SCRATCH/dummy

%  lfs getstripe $SCRATCH/dummy | grep lmm
lmm_stripe_count:  8
lmm_stripe_size:   1048576
lmm_pattern:       raid0,overstriped
lmm_layout_gen:    0
lmm_stripe_offset: 10
lmm_pool:          original

My understanding is when without overstriping, the default is that
the OSTs are selected by Lustre MDS based on some policy (maybe OST
usage). I wonder if this can also apply to overstriping, i.e. using
lfs command options '-c' and '-C' without option '-o'.

I am also wondering how this can be achieved using the Lustre user
C APIs, when making calls to llapi_layout_ost_index_set().


Wei-keng