On 01/01/17 22:38, Andrei Borzenkov wrote:
As I understand btrfs, "hot spare" is a meaningless term. Given that
btrfs understands the concept of a filesystem spanning multiple drives, if a drive fails underneath it any files which have been declared as "mirrored" and have a copy on the failed drive, will have suddenly become "single copy" so the file system needs to replicate them onto another drive.
Which is exact definition of "hot spare". Drive that is used to restore redundancy *automatically*, without involving manual actions. I do not see what magic in btrfs suddenly makes it "meaningless".
Which actually it is most definitely *N*O*T* the definition of a hot spare. Where in my definition does it even imply the existence of a SPARE disk, let alone a hot spare? Which is why I said the concept of a hot spare in the context of btrfs is meaningless. There is spare space on a hot drive. There is no spare drive which is hot. Let's explain, nice and simple. We'll assume we have a btrfs file system spanning three drives, A, B, and C. We have a root directory a, two subdirectories b and c, and four files b1, b2, c1, c2. The structure is such that a is recursively mirrored. That means that a copy of a exists on A and B. b exists on C and A, c exists on B and C, etc etc. Now which drive is the hot spare? Yet the entire directory structure is mirrored across the three drives, such that any single failure can be recovered from. (Oh, and by the way, this exact sort of structure is one of the raid structures supported by mdraid, iirc.) Cheers, Wol -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org