Hi Qu Thanks for your reply. That's really helpful. BTW, I just read this url and the mail thread in it. https://unix.stackexchange.com/a/345972 It seems to say if raid1 is degraded and even if rw, it should not be applied any operations other than btrfs-replace or btrfs-balance. Does it mean the degraded raid1 should not be used with both btrfs-replace/balance and the original server rw services at the meantime? For example, I put PostgreSQL DB on btrfs raid1 and I though one of raid1 two copies is my backup. Even if I lost one copy, the service still can keep running by another one immediately. Okay, maybe not immediately. I need to reboot. But waiting 24 hours or longer which depends on the size of data for the completion of btrfs-replace/balance seems not to be a good idea. Regards, Chiung-Ming Huang Regards, Chiung-Ming Huang Qu Wenruo <quwenruo.btrfs@xxxxxxx> 於 2020年2月10日 週一 下午3:03寫道： > > > > On 2020/2/10 下午2:50, Chiung-Ming Huang wrote: > > Qu Wenruo <quwenruo.btrfs@xxxxxxx> 於 2020年2月7日 週五 下午3:16寫道： > >> > >> > >> > >> On 2020/2/7 下午2:16, Chiung-Ming Huang wrote: > >>> Qu Wenruo <quwenruo.btrfs@xxxxxxx> 於 2020年2月7日 週五 下午12:00寫道： > >>>> > >>>> All these subvolumes had a missing root dir. That's not good either. > >>>> I guess btrfs-restore is your last chance, or RO mount with my > >>>> rescue=skipbg patchset: > >>>> https://patchwork.kernel.org/project/linux-btrfs/list/?series=170715 > >>>> > >>> > >>> Is it possible to use original disks to keep the restored data safely? > >>> I would like > >>> to restore the data of /dev/bcache3 to the new btrfs RAID0 at the first and then > >>> add it to the new btrfs RAID0. Does `btrfs restore` need metadata or something > >>> in /dev/bcache3 to restore /dev/bcache2 and /dev/bcache4? > >> > >> Devid 1 (bcache 2) seems OK to be missing, as all its data and metadata > >> are in RAID1. > >> > >> But it's strongly recommended to test without wiping bcache2, to make > >> sure btrfs-restore can salvage enough data, then wipeing bcache2. > >> > >> Thanks, > >> Qu > > > > Is it possible to shrink the size of bcache2 btrfs without making > > everything worse? > > I need more disk space but I still need bcache2 itself. > > That is kinda possible, but please keep in mind that, even in the best > case, it still needs to write some (very small amount) metadata into the > fs, thus I can't ensure it won't make things worse, or even possible > without falling back to RO. > > You need to dump the device extent tree, to determine the where the last > dev extent is for each device, then shrink to that size. > > Some example here: > > # btrfs ins dump-tree -t dev /dev/nvme/btrfs > ... > > item 6 key (1 DEV_EXTENT 2169503744) itemoff 15955 itemsize 48 > dev extent chunk_tree 3 > chunk_objectid 256 chunk_offset 2169503744 length 1073741824 > chunk_tree_uuid 00000000-0000-0000-0000-000000000000 > > Here for the key, 1 means devid 1, 2169503744 means where the device > extent starts at. 1073741824 is the length of the device extent. > > In above case, the device with devid 1 can be resized to 2169503744 + > 1073741824, without relocating any data/metadata. > > # time btrfs fi resize 1:3243245568 /mnt/btrfs/ > Resize '/mnt/btrfs/' of '1:3243245568' > > real 0m0.013s > user 0m0.006s > sys 0m0.004s > > And the dump-tree shows the same last device extent: > ... > item 6 key (1 DEV_EXTENT 2169503744) itemoff 15955 itemsize 48 > dev extent chunk_tree 3 > chunk_objectid 256 chunk_offset 2169503744 length 1073741824 > chunk_tree_uuid 00000000-0000-0000-0000-000000000000 > > (Maybe it's a good time to implement some like fast shrink for btrfs-progs) > > Of course, after resizing btrfs, you still need to resize bcache, but > that's not related to btrfs (and I am not familiar with bcache either). > > Thanks, > Qu > > > > > Regards, > > Chiung-Ming Huang > > > > > >>> > >>> /dev/bcache2, ID: 1 > >>> Device size: 9.09TiB > >>> Device slack: 0.00B > >>> Data,RAID1: 3.93TiB > >>> Metadata,RAID1: 2.00GiB > >>> System,RAID1: 32.00MiB > >>> Unallocated: 5.16TiB > >>> > >>> /dev/bcache3, ID: 3 > >>> Device size: 2.73TiB > >>> Device slack: 0.00B > >>> Data,single: 378.00GiB > >>> Data,RAID1: 355.00GiB > >>> Metadata,single: 2.00GiB > >>> Metadata,RAID1: 11.00GiB > >>> Unallocated: 2.00TiB > >>> > >>> /dev/bcache4, ID: 5 > >>> Device size: 9.09TiB > >>> Device slack: 0.00B > >>> Data,single: 2.93TiB > >>> Data,RAID1: 4.15TiB > >>> Metadata,single: 6.00GiB > >>> Metadata,RAID1: 11.00GiB > >>> System,RAID1: 32.00MiB > >>> Unallocated: 2.00TiB > >>> > >>> Regards, > >>> Chiung-Ming Huang > >>> > >> >
