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Re: Split some metadata onto separate device?

Hi Ryusuke,

On Friday 03 June 2011 19:26:21 you wrote:
> (...) 
> NILFS2 is a log-structured filesystem and that means the filesystem
> itself is a big journal.  My understanding is using separate journal
> device has no merit of performance.
> On the other hand, We may be able to speed up the filesystem by
> putting DAT (disk address translation) metadata to a separate device.
> I mean putting a full copy of the DAT metadata on the sperate device
> instead of journal of it.

*nods* sounds interesting. Of course changing on-disk format would hurt ;-)

> But, I think we have other approaches to think about before that with
> regard to performance improvement.  For example, applying "extent" to
> DAT seems much more effective.

Currently every block of file gets own entry in DAT, right?

By the way, it seems to me that the in-kernel GC does not attempt to de-
fragment files. Is that the case? If so, would probably mean extents would not 
help very much for fragmented files. Also, on magnetic media, a lot of seeking 
happens in case of fragmented files.

dexen deVries

``One can't proceed from the informal to the formal by formal means.''
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