[Lustre-discuss] "obdidx" ordering in "lfs getstripe"

[Jack David]

Hi All,

In the output of "lsf getstripe <filename> | <dirname>", the obdidx
denotes the OST index (I assume).

Consider the following output:

lmm_stripe_count:   2
lmm_stripe_size:    1048576
lmm_stripe_offset:  1
	obdidx		 objid		objid		 group
	     1	             2	          0x2	             0
	     0	             3	          0x3	             0

where I have a setup consisting of two OSTs. If I have more than two
OSTs, is it possible that I get the obdidx values out of order? Or the
obdidx values will always be linear?

For example, in above output, the values are linear (like 1, 0 - and
this pattern will be repeated while storing the data I assume). If I
have 4 OSTs, can the values be non-linear? Something like 2,0,1,3 or
2,1,3,0 (or any pattern for that matter)??

My assumption on how the data is stored on OSTs:
Based upon the values of obdidx, each OST will store a stripe_size
worth data into the objid (a file under ldiskfs volume of that OST) in
rotation. So if I get the obdidx like 2,1,3,0 and stripe_size if 1MB,
then the data will be stored in following order:

1st MB: 2nd OST
2nd MB: 1st OST
3rdMB: 3rd OST
4thMB: 0th OST
5th MB: 2nd OST (Again - repeating the pattern)
6th MB: 1st OST

Is this understanding correct?? I hope I am clear on my question.


Thanks,
J