Now that I actually started to invistigate the problem myself in earnest, I am really getting to know my Synology DiskStation quite a bit.
Part of the process is to familiarize myself with the layout of the system and the various command line utilities available for inspecting status and history. Surely there are quite a few graphical tools which come as part of the operating system, but you really want to drill down on details there is not other way than to get in there via the terminal.
Nicely enough the DiskStation Manager (DSM) is based on the Linux Kernel, thereby resulting in a directory layout for the system, which is rather familiar. So with a little bit of reading up and exploring it is possible to find the relevant configuration files and inspection tools. So after poking around a bit, here is where I am at right now:
(a) Check log with system messages
Going through the entries of
/var/log/messages I noticed that the system failed
to assemble the volume associatd with
/dev/md4, which I guess is my main data
volume (the one currently labeled as “crashed”).
Dec 28 12:29:05 DiskStation spacetool.shared: spacetool.c:1069 Try to force assemble RAID [/dev/md4]. [0x8000 raid_ioctl_info.c:55] Dec 28 12:29:05 DiskStation spacetool.shared: raid_allow_rmw_check.c:48 fopen failed: /usr/syno/etc/.rmw.md6 Dec 28 12:29:06 DiskStation kernel: [ 56.303999] md: md5: current auto_remap = 0 Dec 28 12:29:06 DiskStation kernel: [ 56.304006] md: reshape of RAID array md5 Dec 28 12:29:06 DiskStation kernel: [ 56.400306] md: md3: current auto_remap = 0 Dec 28 12:29:06 DiskStation spacetool.shared: raid_allow_rmw_check.c:35 Failed to get RAID '/dev/md4' info. Dec 28 12:29:06 DiskStation spacetool.shared: raid_enable_multithread.c:42 Failed to get RAID '/dev/md4' info. Dec 28 12:29:06 DiskStation spacetool.shared: spacetool.c:1097 Fail to enable multithread of [/dev/md4] Dec 28 12:29:09 DiskStation spacetool.shared: spacetool.c:2835 [Info] Old vg path: [/dev/vg1000], New vg path: [/dev/vg1000], UUID: [ThEUxo-6Fl7-3hp0-dBir-xQE6-TRE1-nmleBS] Dec 28 12:29:09 DiskStation spacetool.shared: spacetool.c:2842 [Info] Activate all VG Dec 28 12:29:10 DiskStation spacetool.shared: lvm_vg_activate.c:23 Failed to do '/sbin/vgchange -ay /dev/vg1000' Dec 28 12:29:10 DiskStation spacetool.shared: spacetool.c:2851 Failed to activate LVM [/dev/vg1000] Dec 28 12:29:10 DiskStation spacetool.shared: spacetool.c:2896 space: [/dev/vg1000] Dec 28 12:29:10 DiskStation spacetool.shared: spacetool.c:2922 space: [/dev/vg1000], ndisk: 
(b) Check on the RAID devices
With the information from the system log next up is a look at the lists of RAID devices and their associated drives/partitions:
As it turns out
md4 indeed is missing from that list, hence little surprise the
volume is not brought up:
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] md5 : active raid5 sdc6 sdb6 sda6 sdk6 sdj6 sdi6 sdg6 sdh6 sdf6 sde6 sdd6 5372034624 blocks super 1.2 level 5, 64k chunk, algorithm 2 [12/11] [UUUUUUU_UUUU] md3 : active raid5 sdh8 sdb8 sdc8 sda8 sdk8 sdj8 sdi8 sdg8 7813942272 blocks super 1.2 level 5, 64k chunk, algorithm 2 [9/8] [UUU_UUUUU] md6 : active raid5 sdc9 sdb9 5860301056 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/2] [UU_] md1 : active raid1 sdl2 sdk2 sdj2 sdi2 sdh2 sdg2 sdf2 sde2 sdd2 sdc2 sdb2 sda2 2097088 blocks [12/12] [UUUUUUUUUUUU] md0 : active raid1 sdl1 sdb1 sda1 sdc1 sdd1 sde1 sdf1 sdg1 sdh1 sdi1 sdj1 sdk1 2490176 blocks [12/12] [UUUUUUUUUUUU] unused devices: <none>
(c) Re-assemble volume
This is the next step now. At the moment I am collecting as much information as I possibly can in order to re-assemble the volume. Part of this effort is reading through contributions on the Online Community Forum – given the fact that the problem I am confronted with seems not to be too uncommon, there is quite some discussion to be found online… hopefully with some pointers into the right direction.