[Tux3] Q: inode numbering, and placement on-disk

Philipp Marek philipp.marek at emerion.com
Wed Feb 25 00:48:46 PST 2009

Hello Daniel,

thank you for your answer.

On Mittwoch, 25. Februar 2009, Daniel Phillips wrote:
> On Wednesday 25 February 2009, Philipp Marek wrote:
> > Now, if I understand Tux3 design correctly, it's no longer the case that
> > the inode numbers have any meaning regarding the on-disk location
> > (because of snapshots, versioning, and other strategies), so this hack
> > (or "feature", if you like) wouldn't work anymore, would it?
> Tux3 does in fact attach significance to inode numbers.  Currently, the
> file data allocation goal (a block number) is used as the inode number
> goal, and Tux3 will assign the next available inode number after that
> to a new file.  In time we will improve this strategy to work well when
> you come back and create a new file in a directory later, most probably
> by maintaining or computing a overall directory allocation goal based
> on physical location of files already in the directory.
That's good to hear.

> As it is now, when you initially write a directory, inode numbers will
> correspond spatially quite well to file data block ordering, but this
> pristine condition will degenerate over time, which can be regarded as
> an optimization bug that needs to be fixed.

Yes; I now looked at http://kerneltrap.org/Linux/Tux3_Hierarchical_Structure, 
and I think I just misunderstood something (or remembered wrong facts).

Now, IIUC, other volumes in the same filesystem get completely distinct inode 
numbers, and if some snapshot gets extended new inodes are used for that, too 
(and these inodes are close to their data again).

Of course that means that their data gets heavily fragmented - some inodes are 
at the start of the device, others in the middle ...
But that's no difference to ext3 or whatever now.

Do you know about any analysis that shows whether keeping directories and 
inodes should be kept closer than inodes and their file-data?

Thank you for your quick answer!



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