On Thu, Dec 31, 2015 at 6:31 AM, Duncan <1i5t5.duncan@xxxxxxx> wrote: > Additionally, if you're going to put btrfs on mdraid, then you may wish > to consider reversing the above, doing raid01, which while ordinarily > discouraged in favor of raid10, has some things going for it when the top > level is btrfs, that raid10 doesn't. Yes, although it's a fine line how to create such a large volume of so many drives. If you use many drives per raid0, when there is a failure it takes a long time to rebuild. If you use few drives per raid0, fast rebuild, but the exposure/risk with a 2nd failure is higher. e.g. two extremes: 12x raid0 "bank A" and 12x raid0 "bank B" If one drive dies, an entire bank is gone, and it's a long rebuild, but if a 2nd drive dies, nearly 50/50 chance it dies in the same already dead bank. 2x raid0 "bank A" and 2x raid0 "bank C" and .... through "bank L" If one drive dies in bank A, then A is gone, short rebuild time, but if a 2nd drive dies, almost certainly it will not be the 2nd bank A drive, meaning it's in another bank and that means the whole array is mortally wounded. Depending on what's missing and what needs to be accessed, it might work OK for seconds, minutes, or hours, and then totally implode. There's no way to predict it in advance. Anyway, I'd sooner go with 3x raid5, or 6x raid6, and then pool them with glusterfs. Even with a single node using replication only for the separate raid5 bricks is more reliable than a 24x raid10 no matter md+xfs or btrfs. That makes it effectively a raid 51. And if half the storage is put on another node, now you have power supply and some network redundancy too. -- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
