Hello/2 all

I'm using libvirt with a qcow2 image and everytime i run btrfs scrub
-H /home (subvolume where the image is), i get:

ago 15 21:58:08 kerberos kernel: BTRFS error (device sda3): bdev
/dev/sda3 errs: wr 0, rd 0, flush 0, corrupt 30, gen 0
ago 15 21:58:08 kerberos kernel: BTRFS error (device sda3): unable to
fixup (regular) error at logical 289831161856 on dev /dev/sda3
ago 15 21:58:08 kerberos kernel: BTRFS error (device sda3): bdev
/dev/sda3 errs: wr 0, rd 0, flush 0, corrupt 31, gen 0
ago 15 21:58:08 kerberos kernel: BTRFS error (device sda3): unable to
fixup (regular) error at logical 289830309888 on dev /dev/sda3
ago 15 21:58:08 kerberos kernel: BTRFS error (device sda3): bdev
/dev/sda3 errs: wr 0, rd 0, flush 0, corrupt 32, gen 0
ago 15 21:58:08 kerberos kernel: BTRFS error (device sda3): unable to
fixup (regular) error at logical 289831055360 on dev /dev/sda3
ago 15 21:58:08 kerberos kernel: BTRFS error (device sda3): bdev
/dev/sda3 errs: wr 0, rd 0, flush 0, corrupt 33, gen 0
ago 15 21:58:08 kerberos kernel: BTRFS error (device sda3): unable to
fixup (regular) error at logical 289861591040 on dev /dev/sda3
ago 15 21:58:09 kerberos kernel: BTRFS warning (device sda3): checksum
error at logical 290297204736 on dev /dev/sda3, sector 67982824, root
258, inode 968837, offset 17455849472, length 4096, links 1 (path:
groo/Fedora/Fedora.qcow2)
ago 15 21:58:09 kerberos kernel: BTRFS error (device sda3): bdev
/dev/sda3 errs: wr 0, rd 0, flush 0, corrupt 34, gen 0
ago 15 21:58:09 kerberos kernel: BTRFS error (device sda3): unable to
fixup (regular) error at logical 290297204736 on dev /dev/sda3

The thing is, as soon as i move the image to another subvolume, root
in this case, and delete it, the errors go away and scrub tells me i
have zero errors again.

Then if i AGAIN copy the file back to /home, i get the same errors.

qemu-img check tells me the qcow2 file is fine, and smart doesnt show
me anything wrong with my ssd:

root@kerberos:/home/groo# smartctl -Ai /dev/sda
smartctl 6.6 2016-05-31 r4324 [x86_64-linux-4.13.0-041300rc4-generic]
(local build)
Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Model Family:     Samsung based SSDs
Device Model:     Samsung SSD 850 EVO M.2 500GB
Serial Number:    S33DNX0H812686V
LU WWN Device Id: 5 002538 d4130d027
Firmware Version: EMT21B6Q
User Capacity:    500.107.862.016 bytes [500 GB]
Sector Size:      512 bytes logical/physical
Rotation Rate:    Solid State Device
Form Factor:      M.2
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   ACS-2, ATA8-ACS T13/1699-D revision 4c
SATA Version is:  SATA 3.1, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Tue Aug 15 21:59:34 2017 -03
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART Attributes Data Structure revision number: 1
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE
UPDATED  WHEN_FAILED RAW_VALUE
  5 Reallocated_Sector_Ct   0x0033   100   100   010    Pre-fail
Always       -       0
  9 Power_On_Hours          0x0032   099   099   000    Old_age
Always       -       1739
 12 Power_Cycle_Count       0x0032   099   099   000    Old_age
Always       -       392
177 Wear_Leveling_Count     0x0013   099   099   000    Pre-fail
Always       -       7
179 Used_Rsvd_Blk_Cnt_Tot   0x0013   100   100   010    Pre-fail
Always       -       0
181 Program_Fail_Cnt_Total  0x0032   100   100   010    Old_age
Always       -       0
182 Erase_Fail_Count_Total  0x0032   100   100   010    Old_age
Always       -       0
183 Runtime_Bad_Block       0x0013   100   100   010    Pre-fail
Always       -       0
187 Uncorrectable_Error_Cnt 0x0032   100   100   000    Old_age
Always       -       0
190 Airflow_Temperature_Cel 0x0032   061   050   000    Old_age
Always       -       39
195 ECC_Error_Rate          0x001a   200   200   000    Old_age
Always       -       0
199 CRC_Error_Count         0x003e   100   100   000    Old_age
Always       -       0
235 POR_Recovery_Count      0x0012   099   099   000    Old_age
Always       -       54
241 Total_LBAs_Written      0x0032   099   099   000    Old_age
Always       -       7997549567

this is the usage for /home:

root@kerberos:/home/groo# btrfs filesystem usage -T /home/
Overall:
    Device size:                 333.50GiB
    Device allocated:             74.12GiB
    Device unallocated:          259.38GiB
    Device missing:                  0.00B
    Used:                         32.70GiB
    Free (estimated):            297.36GiB      (min: 167.67GiB)
    Data ratio:                       1.00
    Metadata ratio:                   2.00
    Global reserve:               58.12MiB      (used: 0.00B)

             Data     Metadata  System
Id Path      single   RAID1     RAID1    Unallocated
-- --------- -------- --------- -------- -----------
 1 /dev/sda3 68.00GiB   2.00GiB 64.00MiB   129.94GiB
 2 /dev/sdb7  2.00GiB   2.00GiB 64.00MiB   128.96GiB
 3 /dev/sdb8        -         -        -   488.13MiB
-- --------- -------- --------- -------- -----------
   Total     70.00GiB   2.00GiB 64.00MiB   259.38GiB
   Used      32.02GiB 348.12MiB 16.00KiB

and for root subvolume:

root@kerberos:/home/groo# btrfs filesystem usage -T /
Overall:
    Device size:                  65.29GiB
    Device allocated:             65.28GiB
    Device unallocated:           12.00MiB
    Device missing:                  0.00B
    Used:                         14.94GiB
    Free (estimated):             48.72GiB      (min: 48.72GiB)
    Data ratio:                       1.00
    Metadata ratio:                   1.00
    Global reserve:               42.20MiB      (used: 0.00B)

             Data     Metadata  System
Id Path      single   single    single   Unallocated
-- --------- -------- --------- -------- -----------
 1 /dev/sda2 63.24GiB   2.01GiB 32.00MiB    12.00MiB
-- --------- -------- --------- -------- -----------
   Total     63.24GiB   2.01GiB 32.00MiB    12.00MiB
   Used      14.52GiB 425.16MiB 16.00KiB

i see this with both kernel 4.12 and 4.13rc4

the btrfstools are:

root@kerberos:/home/groo# btrfs version
btrfs-progs v4.12-dirty

/etc/fstab:

UUID=e31faa09-99e5-4c75-815c-629402ec92f2 /               btrfs
defaults,discard,subvol=@ 0       1
# /boot was on /dev/sda1 during installation
UUID=55796428-a9b8-4f1b-9a7e-8fe3aa8d8097 /boot           ext4
defaults        0       2
# /boot/efi was on /dev/sdb2 during installation
UUID=D4F8-9F87  /boot/efi       vfat    umask=0077      0       1
# /home was on /dev/sda3 during installation
UUID=ae9ae869-720d-4643-b673-6924d09b2fe0 /home           btrfs
defaults,discard,subvol=@home 0       2
# swap was on /dev/sdb6 during installation
#UUID=fc2a432b-4c40-4fe4-9730-869a1d1911ef none            swap    sw
            0       0
/dev/mapper/cryptswap1 none swap sw 0 0


this is reproducible every single time.

is btrfs scrub maybe getting confused with a sparse file? is it
possible to get a bad checksum with raid1 in this scenario?

any help is appreciated

| Paulo Dias
| paulo.miguel.d...@gmail.com

Tempora mutantur, nos et mutamur in illis.
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