So this is interesting:
[ 688.925196] sd 0:0:0:0: [sda] UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[ 688.925212] sd 0:0:0:0: [sda] Sense Key : 0x3 [current]
[ 688.925219] sd 0:0:0:0: [sda] ASC=0x11 ASCQ=0x0
[ 688.925228] sd 0:0:0:0: [sda] CDB: opcode=0x28 28 00 00 60 08 48 00 00 08 00
[ 688.925236] blk_update_request: critical medium error, dev sda, sector 6293576
[ 688.925891] sd 0:0:0:0: [sda] UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[ 688.925899] sd 0:0:0:0: [sda] Sense Key : 0x3 [current]
[ 688.925906] sd 0:0:0:0: [sda] ASC=0x11 ASCQ=0x0
[ 688.925914] sd 0:0:0:0: [sda] CDB: opcode=0x28 28 00 00 60 08 48 00 00 08 00
[ 688.925920] blk_update_request: critical medium error, dev sda, sector 6293576
[ 688.925928] Buffer I/O error on dev sda1, logical block 786441, async page read
[ 688.927685] sd 0:0:0:0: [sda] UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[ 688.927699] sd 0:0:0:0: [sda] Sense Key : 0x3 [current]
[ 688.927706] sd 0:0:0:0: [sda] ASC=0x11 ASCQ=0x0
[ 688.927715] sd 0:0:0:0: [sda] CDB: opcode=0x28 28 00 00 01 89 68 00 00 08 00
[ 688.927723] blk_update_request: critical medium error, dev sda, sector 100712
[ 688.928421] sd 0:0:0:0: [sda] UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[ 688.928432] sd 0:0:0:0: [sda] Sense Key : 0x3 [current]
[ 688.928439] sd 0:0:0:0: [sda] ASC=0x11 ASCQ=0x0
[ 688.928448] sd 0:0:0:0: [sda] CDB: opcode=0x28 28 00 00 01 89 68 00 00 08 00
[ 688.928455] blk_update_request: critical medium error, dev sda, sector 100712
[ 688.928463] Buffer I/O error on dev sda1, logical block 12333, async page read
[ 688.937289] sd 0:0:0:0: [sda] UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[ 688.937304] sd 0:0:0:0: [sda] Sense Key : 0x3 [current]
[ 688.937311] sd 0:0:0:0: [sda] ASC=0x11 ASCQ=0x0
[ 688.937321] sd 0:0:0:0: [sda] CDB: opcode=0x28 28 00 00 60 08 48 00 00 08 00
[ 688.937346] blk_update_request: critical medium error, dev sda, sector 6293576
[ 688.937355] Buffer I/O error on dev sda1, logical block 786441, async page read
[ 688.938240] sd 0:0:0:0: [sda] UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
[ 688.938252] sd 0:0:0:0: [sda] Sense Key : 0x3 [current]
[ 688.938259] sd 0:0:0:0: [sda] ASC=0x11 ASCQ=0x0
[ 688.938269] sd 0:0:0:0: [sda] CDB: opcode=0x28 28 00 00 01 89 68 00 00 08 00
[ 688.938276] blk_update_request: critical medium error, dev sda, sector 100712
[ 688.938284] Buffer I/O error on dev sda1, logical block 12333, async page read
And mount:
/dev/mmcblk0p2 on / type ext4 (rw,noatime,data=ordered)
devtmpfs on /dev type devtmpfs (rw,relatime,size=469688k,nr_inodes=117422,mode=755)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
proc on /proc type proc (rw,relatime)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k)
tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755)
cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd)
cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)
cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpu,cpuacct)
cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
cgroup on /sys/fs/cgroup/net_cls type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=22,pgrp=1,timeout=300,minproto=5,maxproto=5,direct)
mqueue on /dev/mqueue type mqueue (rw,relatime)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
configfs on /sys/kernel/config type configfs (rw,relatime)
fusectl on /sys/fs/fuse/connections type fusectl (rw,relatime)
/dev/mmcblk0p1 on /boot type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,errors=remount-ro)
/dev/sda1 on /mnt/sda1 type fuseblk (rw,nosuid,nodev,noexec,relatime,user_id=0,group_id=0,allow_other,blksize=4096)
tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=94804k,mode=700,uid=1000,gid=1000)
gvfsd-fuse on /run/user/1000/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000)