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

Andreas Dilger adilger at sun.com
Tue Nov 17 09:34:03 PST 2009


On 2009-11-17, at 09:13, Geoff Lustre wrote:
> Thanks for the correction. Your point was made clearly enough  
> though!  One more question which I feel will be of interest to more  
> than just me.
>
> Any reason the inode maxes out at 2k? 4k is perfectly possible.

One problem that used to be hit with 4k inodes is that the block size
is also 4k, and the default filesystem configuration is to have one
inode for each block in the filesystem.  That means that the inode
table would consume all of the blocks in the filesystem, leaving no
space for other (meta)data like the journal, directories, etc.

This used to cause mke2fs to spin forever trying to find free space
in the filesystem.

Secondly, it is very uncommon to have a filesystem with a default
stripe size of 160, so this is generally not hit.

Finally, even if the inode size is 4kB, this leaves 4096-128 bytes
of space for extended attributes, which isn't enough to hold a fully
striped file (160 stripes) and there will not be much/any space left
in the filesystem to store external xattrs.

Instead, it is better to create a smaller inode, and for the lower
percentage of files that have a lot of stripes they will use external
xattr blocks to store the striping data.

> On Tue, Nov 17, 2009 at 2:50 PM, Brian J. Murrell <Brian.Murrell at sun.com 
> > wrote:
> On Mon, 2009-11-16 at 16:26 -0500, Brian J. Murrell wrote:
>
> A correction to my posting of yesterday...
>
> > 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
>             ^^^^
> This should be 512 byte inode.
>
> Apologies for the cut'n'pasto.
>
> b.
>
>
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Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.




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