Comment # 2 on bug 992256 from Jeff Mahoney

[ 6170.336545] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 1,
flush 0, corrupt 0, gen 0
[ 6170.336566] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 2,
flush 0, corrupt 0, gen 0
[ 6170.336590] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 3,
flush 0, corrupt 0, gen 0
[ 6170.336599] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 4,
flush 0, corrupt 0, gen 0
[ 6170.341917] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 5,
flush 0, corrupt 0, gen 0
[ 6170.342358] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 6,
flush 0, corrupt 0, gen 0
[ 6170.343008] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 7,
flush 0, corrupt 0, gen 0
[ 6170.343221] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 8,
flush 0, corrupt 0, gen 0
[ 6170.343319] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 9,
flush 0, corrupt 0, gen 0
[ 6170.343330] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 10,
flush 0, corrupt 0, gen 0
[ 6175.338176] btrfs_dev_stat_print_on_error: 386734 callbacks suppressed
[ 6175.338180] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386745,
flush 0, corrupt 0, gen 0
[ 6175.338190] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386746,
flush 0, corrupt 0, gen 0
[ 6175.338207] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386747,
flush 0, corrupt 0, gen 0
[ 6175.338215] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386748,
flush 0, corrupt 0, gen 0
[ 6175.338230] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386749,
flush 0, corrupt 0, gen 0
[ 6175.338239] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386750,
flush 0, corrupt 0, gen 0
[ 6175.338257] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386751,
flush 0, corrupt 0, gen 0
[ 6175.338265] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386752,
flush 0, corrupt 0, gen 0
[ 6175.338283] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386753,
flush 0, corrupt 0, gen 0
[ 6175.338291] BTRFS error (device sdb1): bdev /dev/sdc1 errs: wr 0, rd 386754,
flush 0, corrupt 0, gen 0
[ 6180.342178] btrfs_dev_stat_print_on_error: 418840 callbacks suppressed


... which looks like *every* block is failing on a read.  If it were a checksum
failure, we should be seeing checksum failures in the log independent of the
read errors.