Re: [osd-dev] [PATCH 7/9] exofs: mkexofs

Jeff Garzik
2009-01-13T13:25:04Z

Benny Halevy wrote:
> IMO the main advantage of moving block allocation down to the OSD target
> is more apparent with distributed file systems a-la pNFS over objects
> where paralleling that task is a key for scalable performance.
>
> The thing is that the target needs to implement its own mapping from
> object logical offsets into disk blocks and this is usually done
> using some kind of a (possibly trimmed down) local file system.
> Therefore the I/O performance of a single OSD is likely to be similar
> to a single file server's.

Well, modern SATA devices are already mini-filesystems internally, when
you consider logical block remapping etc.

And the claim by drive research guys at the filesystem/storage summit
was that OSD offered the potential to better optimize storage based on
access/usage patterns.

(of course, whether or not reality bears out this guess is another question)

> I can understand representing a single object as a block device (although I
> think that using a file for that should be good enough and easier) but
> why representing the whole OSD as a block device? The OSD holds partitions
> and objects each with attributes and OSD security related support. Hence
> representing that in a namespace using a filesystem seems straight forward.

I am actually considering writing a simple "osdblk" driver, that would
represent a single object as a block device.

This would NOT replace exofs or other OSD filesystems, but it would be
nice to have, and it will give me more experience with OSDs.

Jeff