[Lustre-discuss] Questions about how inodes origanized in Lustre

[Andreas Dilger]

On 2011-04-18, at 8:15 PM, Johnny R wrote:
>   Excuse me for my ignorance,I'm a newbie in Lustre,and I'm planning to organize the inodes in the MDS used  B-tree.
>   And now I am confused about how things are worked in Lustre.

Lustre itself doesn't handle directly the on-disk layout for directories.  That is done using a patched version of ext4, so if you want to do any development with b-trees you can mostly just do it against ext4.

That said, you should look at the "IAM" patch in ldiskfs as a starting point.  It is essentially implementing btree layout for ext4, but it was never put into production because it didn't include e2fsck support, changed the on-disk layout, and the benefits of it are largely achievable with in-kernel changes.

See also the recent presentation about metadata server scaling with pdirops for ext4 http://wiki.whamcloud.com/download/attachments/7634983/Lustre-MDPI.pdf?version=1&modificationDate=1302720127630 slides 16-18, and the patch in Gerrit at http://review.whamcloud.com/#change,375.  This is more likely to be the path forward, since it avoids any need to change the underlying filesystem format.

>   I use version 1.4.8,and there is fs.h fs.c inode.h inode.c in the Lustre source files.

Sorry, but any work done on Lustre 1.4 is completely pointless.  You should start with 1.8.5 or the pre-1.8.6 code from git.lustre.org.  If you are doing anything for actual inclusion into future Lustre releases, it is best to do it from the pre-2.1 code at git.whamcloud.com.

>   But when I look up the Lustre arrchives,I find that Lustre seems to use llite to manage the inode part.
>   Looking forward to your answers.
>                                                                                                                            Johnny R
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Cheers, Andreas
--
Andreas Dilger 
Principal Engineer
Whamcloud, Inc.