[Lustre-discuss] mkfs.lustre stripe-count-hint

Geoff Lustre lustre at keywordtraining.it
Mon Nov 16 13:03:09 PST 2009


Dear Friends

My understanding of this parameter is:

It provides the mkfs.lustre command with a hint about the expected level of
striping.  The larger the (expected) stripe, the larger the resulting
inodes. This allows (more) EAs to be embedded in the inode, allowing one
read to bring the inode including EAs into memory. Small inodes have the EAs
located at the other end of a pointer, casing two seeks to bring the EAs
into memory.

So much for the theory.  With Lustre 1.8.1 the output from the mkfs.lustre
 with no stripe-count-hint and the output with stripe-count-hint =160 is the
same.  The inode size in both cases appears to be 512 bytes (viz -I 512).
This result is also true in 1.8.1.1.

Is stripe-count-hint ignored, as appears to be the case?

It is possible to use --mkfsoptions="-I 4096 -i 4608" to force the creation
of 4k inodes. (This is the largest permissible size).  Please would someone
confirm (or deny) the larger inode size has the effect of allowing lustre to
handle inodes for heavily striped files more efficiently?


Regards


Geoff carrier
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