On Thu, Aug 27, 2015 at 11:32 AM, carlo von lynX <lynX@xxxxxxxxxxxxxxxxxxxxxx> wrote: > Hi there. Excuse me if I didn't subscribe the list. Just wanted to > let you know of this behavior assuming you haven't noticed it yet. > > When mounting two copies of the same file system from two different > hard disks with the intention of syncing the older with the newer > one, btrfs behaves differently from ext4: it will mount the first > one twice rather than mounting each. I assume it has something to > do with all UUIDs being identical, which doesn't disturb ext4 though. I'd say any file system that allows mount without warning when two fs volumes with the same UUID is a bug. I vastly prefer the XFS behavior in this regard which is warn and refusal to mount. You have to use -o nouuid to make it happen; and then I guess there's some separate handling to still keep the fs instances separate, but I don't know how that works at all or how ext4 and Btrfs differ. > This only happens with btrfs - I cannot mount two file systems that > happen to have the same UUID (or are deemed identical by some other > criterion I cannot determine). I presume this is not intended > behavior. I tried relabeling one of the copies, but it didn't have > any effect. Nope, it really can't work. I haven't tried it but I suspect that with XFS v5 that it's not possible either. > Now I'm looking into ways to change the UUID. This is in the current version of btrfs-progs with the btrfs-tune command. -- 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
