On Wednesday May 31, davidsen@xxxxxxx wrote: > Where I was working most recently some systems were using RAID5E (RAID5 > with both the parity and hot spare distributed). This seems to be highly > desirable for small arrays, where spreading head motion over one more > drive will improve performance, and in all cases where a rebuild to the > hot spare will avoid a bottleneck on a single drive. > > Is there any plan to add this capability? I thought about it briefly.... As I understand it, the layout of raid5e when non-degraded is very similar to raid6 - however the 'Q' block is simply not used. This would be trivial to implement. The interesting bit comes when a device fails and you want to rebuild that distributed spare. There are two possible ways that you could do this: 1/ Leave the spare where it is and write the correct data into each spare. This would be fairly easy but would leave an array with an very ... interesting layout of data. When you add a replacement you just move everything back. 2/ reshape the array to be a regular raid5 layout. This would be hard to do well without NVRAM as you are moving live data, but would result in a neat and tidy array. Ofcourse adding a drive back in would be interesting again... I had previously only thought of option '2', and so discarded the idea as not worth the effort. The more I think about it, the more possible option 1 sounds. I've put it back on my todo list, but I don't expect to get to it this year. Ofcourse if someone else wants to give it a try, I'm happy to make suggestions and review code. NeilBrown - 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
