On 31/05/2013 08:30, Roman Mamedov wrote:

On Thu, 30 May 2013 22:23:59 +0100
Dominic Raferd [off-list ref] wrote:

quoted

I am wanting to (re)set up my raid1 array with 1 SSD partition
(/dev/sda2) and 1 'rust' drive partition (/dev/sdb1) , both 240GB. SSD

Sorry but what is "Rust drive partition"? At first I thought it's some
software layer like 'bcache' or some other non-regular block device. Then I
think I got it, but can you please leave at home your own petty cutesy
terminology when asking a serious question on a serious mailing list?

Sorry no offence intended! I just mean a conventional spinning platter 
hard disk drive.

And yes I use a HDD+SSD RAID1 for a very long time, to get some improvement
(though debatable how much) you can also mark the HDD as "write-mostly"
(see man md).

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