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Re: Problem identified: WAPL/RAIDframe performance problems

On Wed, Nov 28, 2012 at 10:24:51PM +0100, J. Hannken-Illjes wrote:
> Flushing is just writing to the log.  These writes have sizes between
> 512 bytes and the file system block size.  Problem is these writes
> are not multiples of and are not aligned to file system block size.

Also issues if they aren't 4k aligned - otherwise the disk itself is likely
to be doing RMW as well.

I must look at how to determine that disks have 4k sectors and to
ensure filesystesm have 4k fragments - regardless of the fs size.

By the sound of it the log ought to be written in fs frag (or block)
sized chunks - even if that means that 'pad' entries get written
in order to flush it to disk after a period of inactivity.


David Laight:

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