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

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Message-ID: <496C9617.80701@garzik.org>
Date:	Tue, 13 Jan 2009 08:24:39 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Benny Halevy <bhalevy@...asas.com>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	open-osd development <osd-dev@...n-osd.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Matthew Wilcox <matthew@....cx>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Avishay Traeger <avishay@...il.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [osd-dev] [PATCH 7/9] exofs: mkexofs

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


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