Hi all, Dne 20.01.2021 v 0:12 Zygo Blaxell napsal(a): > With the 4 device types we can trivially specify this arrangement. > > The sorted device lists would be: > > Metadata sort order Data sort order > metadata only (3) data only (2) > metadata preferred (1) data preferred (0) > data preferred (0) metadata preferred (1) > other devices (2 or other) other devices (3 or other) > > We keep 3 device counts for the first 3 sort orders. If the number of all > preferred devices (type != 0) is zero, we just return ndevs; otherwise, > we pick the first device count that is >= mindevs. If all the device > counts are < mindevs then we return the 3rd count (metadata only + > metadata preferred + data preferred) and the caller will find ENOSPC. > > More sophisticated future implementations can alter the sort order, or > operate in entirely separate parts of btrfs, without conflicting with > this scheme. If there is no mount option, then future implementations > can't conflict with it.
I agree with Zygo and Josef that the mount option is ugly and needless. This should be a _per-device_ setting as suggested by Zygo (metadata only, metadata preferred, data preferred, data only, unspecified). Maybe in the future it might be useful to generalize this setting to something like a 0..255 priority but the 4 device types look like a sufficient solution for now. I would personally prefer a read-write sysfs option to change the device preference but btrfs-progs approach is fine for me too. Anyway, I'm REALLY happy that there's finally a patchset being actively discussed. I maintain a naive patch implementing "preferred_metadata=metadata" option for years and the impact e.g. for rsync backups is huge. Martin
