Mark Murawski posted on Wed, 17 Sep 2014 13:51:51 -0400 as excerpted: >> Does/should a balance imply removal of missing devices (as long as >> the minimum number of devices are still available)? > > That's a really good question. As a user I would expect it to balance > over remaining devices assuming you still have a complete picture. Doing > a device delete missing after a balance should be just some pool > metadata updates at that point. A balance does not imply removal of missing devices. And at this point I'd say it shouldn't, tho perhaps some day after the code is somewhat more stable it could. In fact, until recently kernelspace btrfs (which does all the work in a balance, userspace is simply the way you tell it what to do) didn't even properly detect dynamically added/removed devices, resulting in definitely unintuitive behavior where the balance would still queue up chunks to be rewritten to the missing device, that would obviously never be written because the device was missing and wasn't coming back! (!!!) AFAIK (I'm a sysadmin and list regular, not a developer) that arguably pathological behavior has been fixed now, at least in theory, and the kernel should properly detect missing devices and should no longer try to write to them when doing a balance, so now, at least in theory and assuming good copies of all data and metadata on the remaining device from the original pair, a balance to it and a just added device in raid1 mode should leave only the device metadata for btrfs device delete missing to fix up afterward. However, as of now, there's still at least two bug reports being traced down in the dynamic device detection code (see the current thread where btrfs fi show on a two-device filesystem is pointing to the wrong place for one of the devices, and another where show says a device is missing, that isn't), and possibly others yet to be found, so it's not yet a good idea to have btrfs doing automatic device delete missing on balance. After the bug fixes are in and the code churn in that area calmed down for a couple kernel cycles, perhaps then we can debate whether a balance should automatically delete missing devices when appropriate, or not, but certainly now isn't isn't the time. -- 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 majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
