[lustre-discuss] overstriping

[John Bauer]

Just a note that the man page for lfs setstripe seems a bit misleading 
for the -C --overstripe-count option.  The man page states "creating > 1 
stripe per OST if count exceeds the number of OSTs in  the file 
system".  It appears that lustre creates more than one stripe on an OST 
if the number of stripes exceeds the number of OSTs in the pool being 
used.  In my example below I selected a pool with 8 OSTs, and striped 16 
wide.  The file system has 64 OSTs.  16 is less than 64, but I still got 
2 stripes per OST.

        -C, --overstripe-count <stripe_count>
               The number of stripes to create, creating > 1 stripe per 
OST if count exceeds the number of OSTs in  the  file
               system.  0  means to use the filesystem-wide default 
stripe count (default 1), and -1 means to stripe over all
               available OSTs.


pfe22.jbauer2 908> lfs setstripe --pool 1_hdd -C 16 this.dat
pfe22.jbauer2 909> lfs getstripe this.dat
this.dat
lmm_stripe_count:  16
lmm_stripe_size:   1048576
lmm_pattern:       raid0,overstriped
lmm_layout_gen:    0
lmm_stripe_offset: 7
lmm_pool:          1_hdd
     obdidx         objid         objid         group
          7          23665469        0x1691b3d                 0
          0          22497141        0x1574775                 0
          4          23541897        0x1673889                 0
          2          23308778        0x163a9ea                 0
          1          23033000        0x15f74a8                 0
          6          23687573        0x1697195                 0
          5          23635915        0x168a7cb                 0
          3          23446533        0x165c405                 0
          7          23665470        0x1691b3e                 0
          0          22497142        0x1574776                 0
          4          23541898        0x167388a                 0
          2          23308779        0x163a9eb                 0
          1          23033001        0x15f74a9                 0
          6          23687574        0x1697196                 0
          5          23635916        0x168a7cc                 0
          3          23446534        0x165c406                 0
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