I had a broken (unmountable) btrfs partition on a USB HDD. The problem had the same error message as described here:https://bbs.archlinux.org/viewtopic.php?id=182505dmesg outputted following[   54.371041] BTRFS: device label BackupMobile devid 1 transid 1420 /dev/dm-3[   54.384764] BTRFS info (device dm-3): disk space caching is enabled[   54.384767] BTRFS: has skinny extents[   54.425187] BTRFS error (device dm-3): bad tree block start 15489378549331356982 932187635712[   54.431990] BTRFS error (device dm-3): bad tree block start 15489378549331356982 932187635712[   54.432025] BTRFS: failed to read tree root on dm-3[   54.449061] BTRFS: open_ctree failed[  199.271168] BTRFS info (device dm-3): enabling auto recovery[  199.271174] BTRFS info (device dm-3): disabling disk space caching[  199.271178] BTRFS: has skinny extents[  199.278451] BTRFS error (device dm-3): bad tree block start 15489378549331356982 932187635712[  199.279109] BTRFS error (device dm-3): bad tree block start 15489378549331356982 932187635712[  199.279119] BTRFS: failed to read tree root on dm-3[  199.279762] BTRFS error (device dm-3): bad tree block start 15489378549331356982 932187635712[  199.280509] BTRFS error (device dm-3): bad tree block start 15489378549331356982 932187635712[  199.280518] BTRFS: failed to read tree root on dm-3[  208.294771] BTRFS: checking UUID treeSmart test passed without issues.I finally fixed the mount-issue by using btrfs-zero-log.Then I could mount the volume again.A day later, I encountered the same problem (unmountable, similar error messages and now even a stacktrace in the log).This time, my problem seems to be fixed by just mounting the partition with recovery options -o recovery. Now I can access my data again and could even write to the disk (though I didn't check integrity of written/saved data). Linux didn't complain, the dmesg log looks like this now:[32382.410416] BTRFS info (device dm-6): disk space caching is enabled[32382.410420] BTRFS: has skinny extentsI could mount the drive several times without issues (through nautilus/GNOME).Is it save to continue using the partition? I would just like to keep the snapshots, otherwise I would have re-formatted already. Despite the still passed Smart test, how can I be sure that it's not a hardware failure and btrfs is to blame?Full dmesg log of a plug-in and mount of the USB HDD in the current state:[32376.048700] usb 3-4: new high-speed USB device number 9 using xhci_hcd[32376.177756] usb 3-4: New USB device found, idVendor=152d, idProduct=0539[32376.177770] usb 3-4: New USB device strings: Mfr=10, Product=11, SerialNumber=5[32376.177773] usb 3-4: Product: USB3.0 to SATA Bridge[32376.177775] usb 3-4: Manufacturer: JMicron[32376.177777] usb 3-4: SerialNumber: XXXXXXXXXXXX[32376.178348] usb-storage 3-4:1.0: USB Mass Storage device detected[32376.178434] usb-storage 3-4:1.0: Quirks match for vid 152d pid 0539: 4000000[32376.178462] scsi host16: usb-storage 3-4:1.0[32377.688528] scsi 16:0:0:0: Direct-Access     ST2000LM 015-2E8174       0000 PQ: 0 ANSI: 2 CCS[32377.689259] sd 16:0:0:0: Attached scsi generic sg2 type 0[32377.699007] sd 16:0:0:0: [sdc] 3907029168 512-byte logical blocks: (2.00 TB/1.82 TiB)[32377.699386] sd 16:0:0:0: [sdc] Write Protect is off[32377.699390] sd 16:0:0:0: [sdc] Mode Sense: 28 00 00 00[32377.699661] sd 16:0:0:0: [sdc] No Caching mode page found[32377.699664] sd 16:0:0:0: [sdc] Assuming drive cache: write through[32377.717199]  sdc: sdc1[32377.729514] sd 16:0:0:0: [sdc] Attached SCSI disk[32382.410416] BTRFS info (device dm-6): disk space caching is enabled[32382.410420] BTRFS: has skinny extentsEdit:As Shiki pointed out, I did a surface scan which seems to be btrfs scrub in the btrfs world. The btrfs scrub log shows 72688 read_errors as well as 72688 uncorrectable_errors. That doesn't look good. I checked against other btrfs hard drives and their scrub logs contained no errors at all.Full log:scrub status:1dc484331-2fb1-49a7-8960-38d0b603bd9f:1|data_extents_scrubbed:85282|tree_extents_scrubbed:130262|data_bytes_scrubbed:5386072064|tree_bytes_scrubbed:2134212608|read_errors:72688|csum_errors:0|verify_errors:0|no_csum:0|csum_discards:0|super_errors:0|malloc_errors:0|uncorrectable_errors:72688|corrected_errors:0|last_physical:7553941504|t_start:1502107169|t_resumed:0|duration:62|canceled:1|finished:1
btrfs still usable after unusual repair?
usb drive;btrfs