I got some time on this today and what I find is not encouraging. First off, one of two smb mounts was not mounting correctly. Then I discover that parts of the system have become read only and ...
and finally dmesg gives a lot of errors ...
Terminal
[ 84.406812] systemd-logind[2931]: Failed to start user service, ignoring: Unk nown unit: user@1000.service
[ 84.487202] systemd-logind[2931]: New session c1 of user xbian.
[ 84.727016] init: wait-for-state (xbmcxbmc-loaded) main process (2574) killed by TERM signal
[ 91.920877] init: xbmc-failed-start main process (527) killed by TERM signal
[ 91.930818] init: wait-for-state (zram-swapxbmc-done) main process (1639) kil led by TERM signal
[ 92.249276] init: ntp main process (4610) terminated with status 1
[ 92.251857] init: mounted-tmp main process (4614) terminated with status 1
[ 92.526839] zram: Added device: zram0
[ 92.539098] zram: Added device: zram1
[ 92.546582] zram: Added device: zram2
[ 92.556261] zram: Added device: zram3
[ 92.734951] zram0: detected capacity change from 0 to 134217728
[ 92.850964] Adding 131068k swap on /dev/zram0. Priority:20 extents:1 across: 131068k SSFS
[ 93.732627] Adding 250876k swap on /dev/mmcblk0p3. Priority:0 extents:1 acro ss:250876k SSFS
[ 93.837618] Adding 250876k swap on /dev/sda2. Priority:0 extents:1 across:25 0876k FS
[ 106.673171] systemd-logind[2931]: New session c2 of user xbian.
[ 144.834867] BTRFS info (device sda1): disk space caching is enabled
[ 145.182856] BTRFS info (device sda1): disk space caching is enabled
[ 242.233587] CIFS VFS: Autodisabling the use of server inode numbers on \\192. 168.1.222\media. This server doesn't seem to support them properly. Hardlinks wi ll not be recognized on this mount. Consider mounting with the "noserverino" opt ion to silence this message.
[ 2165.936871] init: xbmc main process (2560) killed by TERM signal
[ 2167.815431] init: wait-for-state (kill-splashxbmc-exits) main process (26474) killed by TERM signal
[ 2181.041520] systemd-logind[2931]: New session c3 of user xbian.
[ 2181.289062] init: wait-for-state (xbmcxbmc-loaded) main process (26542) kille d by TERM signal
[ 2672.592448] init: xbmc-priority main process (32252) terminated with status 1
[ 2908.154952] systemd-logind[2931]: New session c4 of user xbian.
[ 2908.426274] init: wait-for-state (xbmcxbmc-loaded) main process (2435) killed by TERM signal
[ 2931.800339] usb 1-1.5: reset high-speed USB device number 5 using dwc_otg
[ 2931.899491] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 1, rd 0, flush 0, corrupt 0, gen 0
[ 2931.899843] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 1, rd 1, flush 0, corrupt 0, gen 0
[ 2931.900001] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 2, rd 1, flush 0, corrupt 0, gen 0
[ 2931.900293] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 3, rd 1, flush 0, corrupt 0, gen 0
[ 2931.900459] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 4, rd 1, flush 0, corrupt 0, gen 0
[ 2931.900502] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 5, rd 1, flush 0, corrupt 0, gen 0
[ 2931.907308] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 5, rd 2, flush 0, corrupt 0, gen 0
[ 2931.909468] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 6, rd 2, flush 0, corrupt 0, gen 0
[ 2931.915573] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 7, rd 2, flush 0, corrupt 0, gen 0
[ 2931.919195] BTRFS error (device sda1): error reading free space cache
[ 2931.919266] BTRFS warning (device sda1): failed to load free space cache for block group 3510632448, rebuilding it now
[ 2931.920987] BTRFS error (device sda1): bdev /dev/sda1 errs: wr 7, rd 3, flush 0, corrupt 0, gen 0
[ 2931.923970] sd 0:0:0:0: [sda] 31260672 512-byte logical blocks: (16.0 GB/14.9 GiB)
[ 2964.233000] usb 1-1.5: reset high-speed USB device number 5 using dwc_otg
[ 2964.354617] sd 0:0:0:0: [sda] 31260672 512-byte logical blocks: (16.0 GB/14.9 GiB)
[ 2996.654037] usb 1-1.5: reset high-speed USB device number 5 using dwc_otg
[ 2998.591240] BTRFS: error (device sda1) in btrfs_commit_transaction:2227: errn o=-5 IO failure (Error while writing out transaction)
[ 2998.591261] BTRFS info (device sda1): forced readonly
[ 2998.591283] BTRFS warning (device sda1): Skipping commit of aborted transacti on.
[ 2998.591294] ------------[ cut here ]------------
[ 2998.591328] WARNING: CPU: 1 PID: 351 at fs/btrfs/transaction.c:1850 btrfs_com mit_transaction+0xa48/0xcd4
[ 2998.591337] BTRFS: Transaction aborted (error -5)
[ 2998.591345] Modules linked in: zram zsmalloc arc4 ecb md4 md5 hmac nls_utf8 s nd_soc_wm8804_i2c snd_soc_wm8804 sg snd_soc_hifiberry_digi snd_soc_bcm2835_i2s s nd_soc_core snd_compress snd_pcm_dmaengine i2c_bcm2835 bcm2835_gpiomem fixed uio _pdrv_genirq uio snd_bcm2835 snd_pcm snd_timer snd cifs evdev rpcsec_gss_krb5 ui nput i2c_dev i2c_bcm2708
[ 2998.591544] CPU: 1 PID: 351 Comm: btrfs-transacti Not tainted 4.9.91+ #1
[ 2998.591553] Hardware name: BCM2835
[ 2998.591592] [<8010fe20>] (unwind_backtrace) from [<8010c320>] (show_stack+0x2 0/0x24)
[ 2998.591617] [<8010c320>] (show_stack) from [<80537ccc>] (dump_stack+0xcc/0x11 0)
[ 2998.591644] [<80537ccc>] (dump_stack) from [<8011d5b4>] (__warn+0xf8/0x110)
[ 2998.591669] [<8011d5b4>] (__warn) from [<8011d614>] (warn_slowpath_fmt+0x48/0 x50)
[ 2998.591694] [<8011d614>] (warn_slowpath_fmt) from [<804107d4>] (btrfs_commit_ transaction+0xa48/0xcd4)
[ 2998.591717] [<804107d4>] (btrfs_commit_transaction) from [<8040b06c>] (transa ction_kthread+0x18c/0x1b0)
[ 2998.591744] [<8040b06c>] (transaction_kthread) from [<8013ccc8>] (kthread+0x1 0c/0x124)
[ 2998.591765] [<8013ccc8>] (kthread) from [<80108394>] (ret_from_fork+0x14/0x20 )
[ 2998.591777] ---[ end trace 25dd3e99ddf5d615 ]---
[ 2998.591793] BTRFS: error (device sda1) in cleanup_transaction:1850: errno=-5 IO failure
[ 2998.591810] BTRFS info (device sda1): delayed_refs has NO entry
[ 2998.645992] BTRFS info (device sda1): delayed_refs has NO entry
[ 4093.748096] BTRFS info (device sda1): disk space caching is enabled
[ 4093.748123] BTRFS error (device sda1): Remounting read-write after error is n ot allowed
[ 4120.233723] BTRFS info (device sda1): disk space caching is enabled
[ 4120.233746] BTRFS error (device sda1): Remounting read-write after error is n ot allowed
[ 4145.545056] BTRFS info (device sda1): disk space caching is enabled
[ 4145.545082] BTRFS error (device sda1): Remounting read-write after error is n ot allowed
[ 4146.810294] BTRFS info (device sda1): disk space caching is enabled
[ 4146.810317] BTRFS error (device sda1): Remounting read-write after error is n ot allowed
[ 4147.893988] BTRFS info (device sda1): disk space caching is enabled
[ 4147.894008] BTRFS error (device sda1): Remounting read-write after error is n ot allowed
[ 4148.730626] BTRFS info (device sda1): disk space caching is enabled
[ 4148.730650] BTRFS error (device sda1): Remounting read-write after error is n ot allowed
Oddly it still all works (except one database not responding) - and this one runs from a usb drive, only boots from sd card. Maybe some corruption from the power cut but I guess I 'll never know for sure.