On Sat, 6 Dec 2014 12:08:37 PM James Harper wrote:
The 'mirror' RAID method of BTRFS is functionally the same as RAID5 from a 'you can lose one disk' point of view. BTRFS makes sure every piece of data is stored on 2 disks, so you can lose any one disk regardless of how big your array is.
The problem is that people assume that btrfs raid1 profile is the same as MD in that all data is on all drives, when it's (sadly) not. With MD you can have a 3 drive mirror and safely lose 2 drives, but with btrfs you can't. It's one thing I'd love to have fixed. I should mention that Miao Xie from Fujitsu is doing a lot of work on the RAID5/6 code, including posting patchsets to implement "Implement device scrub/replace for RAID56" which is important. All the best, Chris -- Chris Samuel : http://www.csamuel.org/ : Melbourne, VIC