[Lustre-discuss] WRT "obdidx ordering in "lfs getstript"

Ms. Megan Larko dobsonunit at gmail.com
Thu Feb 9 17:49:56 PST 2012


I was reading Mr. David's query about the ordering of data on a
striped luster file system.   I too am under the impression that the
data stripe of size lfs-stripesize will rotate in order from the
starting point.    Following Mr. David's example, a large data set
would be written to the 2nd OST, with the next piece on the 3rd, then
0th and finally 1st before circling back around to the 2nd (assuming
OSTs 0 to 3 from the example).  In his response, Mr. Dilger stated:
"when OST free space is imbalanced  the OSTs will be selected in part
based on how full they are".   Does that refer to a starting point for
the data writes before the orderly progression?   Does that somehow
imply a "skipping over" of a "full" OST?    The latter would be
revolutionary to me in my personal understanding of Lustre and cluster
file systems in general.   I thought that a single OST having
insufficient space available for writing of the data piece of "stripe
size"---or all of the data if the default Lustre stripe size of one is
used--would cause a file system full error.    This error can confuse
users and novice administrators who see a file system full message
when a typical disk usage command on the client will show (ofter a
reasonable) percentage available on the file system as a whole.

Have I misunderstood something here or is this skipping over a full
OST something in the newer versions of Lustre cluster filesystem?


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