[Lustre-discuss] mkfs.lustre stripe-count-hint
Brian J. Murrell
Brian.Murrell at Sun.COM
Mon Nov 16 13:26:21 PST 2009
On Mon, 2009-11-16 at 21:03 +0000, Geoff Lustre wrote:
>
> My understanding of this parameter is:
>
>
> It provides the mkfs.lustre command with a hint about the expected
> level of striping.
Yes, indeed.
> The larger the (expected) stripe, the larger the resulting inodes.
To a limit, yes. See bug 7240/7241.
> This allows (more) EAs to be embedded in the inode, allowing one read
> to bring the inode including EAs into memory.
Yes, that's the theory.
> Small inodes have the EAs located at the other end of a pointer,
> casing two seeks to bring the EAs into memory.
Correct.
> 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.
That's right. Because 160 is at the other end of the scale.
> Is stripe-count-hint ignored, as appears to be the case?
No. The algorithm is as such:
if the stripe-count hint > 72, then 512 byte inode
if the stripe-count hint > 32, then 2048 byte inode
if the stripe-count hint > 10, then 1024 byte inode
otherwise, 1024 byte inode
Where the last match wins.
> It is possible to use --mkfsoptions="-I 4096 -i 4608" to force the
> creation of 4k inodes.
Yes.
> (This is the largest permissible size).
Correct.
> 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?
It does, with a cost as outlined by bug 7240/7241.
b.
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