Hi, On Fri, Oct 11, 2013 at 10:42:07AM +0200, David Brown wrote: > Then for each pair of SSD, make a triple mirror with the two SSD's, and > a "write-mostly" hard disk raid partition. All writes will be then get > an extra copy on the hard disk, while reads will always come from the > SSD's, and therefore be at the same low latency and high speed as > before, and will not use up the HD's bandwidth on reads. And if both > your SSD's die, you have the extra copy on the hard disk. It will run > like treacle, but it will run. I've done that and found some bugs. Neil has already fixed that btw :-). Write-mostly with a write-behind works mostly correct, all O will be lagging waiting for the disk to catch up, but reads are really really fast. In our case we had a single hard disk paired with a single SSD. The blade could not hold more and we were not confident enough with SSD. Well, if the SSD breaks, so does your server, but then of high load ;-). (Actually the server doesn't break, but your application will). Personally I would try a raid-1 with two different manufacturers SSD (or some brands you have really tested under continuous high load), bcache and then the old array. And I mean try: as in have a redundant setup. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
