Russell Coker posted on Thu, 15 May 2014 19:00:10 +1000 as excerpted: > http://www.cs.wisc.edu/adsl/Publications/corruption-fast08.html > > Page 13 of the above paper says: > > # Figure 12 [...] We see in the figure that many disks develop > # corruption for a specific set of block numbers. [T]herefore, > # RAID system designers may be well-advised to use staggered > # stripes such that the blocks that form a stripe (providing > # the required redundancy) are placed at different block numbers > # on different disks. > > Does the BTRFS RAID functionality do such staggered stripes? If not > could it be added?
AFAIK nothing like that yet, but it's reasonably likely to be implemented later. N-way-mirroring is roadmapped for next up after raid56 completion, however. You do mention the partition alternative, but not as I'd do it for such a case. Instead of doing a different sized buffer partition (or using the mkfs.btrfs option to start at some offset into the device) on each device, I'd simply do multiple partitions and reorder them on each device. Tho N-way-mirroring would sure help here too, since if a given area around the same address is assumed to be weak on each device, I'd sure like greater than the current 2-way-mirroring, even if if I had a different filesystem/partition at that spot on each one, since with only two-way-mirroring if one copy is assumed to be weak, guess what, you're down to only one reasonably reliable copy now, and that's not a good spot to be in if that one copy happens to be hit by a cosmic ray or otherwise fail checksum, without another reliable copy to fix it since that other copy is in the weak area already. Another alternative would be using something like mdraid's raid10 "far" layout, with btrfs on top of that... -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
