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Re: FFS write coalescing

On Mon, Dec 03, 2012 at 06:21:30PM +0100, Edgar Fu? wrote:
> When FFS does write coalescing, will it try to align the resulting 64k chunk?
> I.e., if I have 32k blocks and I write blocks 1, 2, 3, 4; will it write (1,2)
> and (3,4) or 1, (2,3) and 4?
> Of course, the background for my question is RAID stripe alignment.

With that thought, for RAID5 in particular, you'd want the FS code
to indicate to the disk that it had some of the nearby data in memory.
That would safe the read of the parity data.
(Which would be really horrid to implement!)

Perhaps the 'disk' should give some 'good parameters' for writes to the
FS code when the filesystem is mounted.


David Laight:

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