On 31/05/2013 08:54, Roman Mamedov wrote:

On Fri, 31 May 2013 08:47:00 +0100
Dominic Raferd [off-list ref] wrote:

quoted

This is my idea too (see my OP), but I am concerned about optimisation
(--write-behind, --bitmap and --bitmap-chunk settings) especially for
writes.
--write-behind=16384

I think this will not work, you will have to use 16383.

Oh, OK, so 16383 is the maximum then?

quoted

--bitmap=/mnt/sda1/write-intent-bitmap.file

Save yourself lots of maintenance headache, just use --bitmap=internal

quoted

--bitmap-chunk=256M

Looks OK.

Thanks Roman, but the problem with using --bitmap=internal is that, as 
Neil Brown posted here on another topic a while ago, this requires a 
synch write to both devices, and the use-case for which write-behind was 
developed involved an external bitmap. Hence my plan to use external 
bitmap file on a fast (SSD-based) separate partition - minimises any 
slow-down caused by having to maintain the write-intent bitmap file.