Just an addition to the solution that I found after I experienced the same issue. I followed dSebastien’s blog post on how to re-create the array:
I found that that method of recreating the array worked better than this above method. However after re-creating the array, the volume was still not showing on the web interface. None of my LUN’s were showing. Basically showing a new array with nothing configured. I contacted Synology support, and they remoted in to fix the issue. Unfortunately, they remoted in whilst I was away from the console. I did manage to capture the session though, and looked through what they did.
Whilst trying to recover some of my data, the drive crashed again, and I was back at the same situation. I recreated the array as in dSebastien’s blog and then looked through the synology session to perform their update. After running the below commands, my array and LUN’s appeared on the web interface, and I was able to work with them. I have practically zero experience in linux, but these were the commands I performed in my situation. Hope this can help someone else, but please use this at your own risk. It would be best to contact Synology support and get them fix this for you, as this situation might be different from yours
DiskStation> synocheckiscsitrg
synocheckiscsitrg: Pass
DiskStation> synocheckshare
synocheckshare: Pass SYNOICheckShare()
synocheckshare: Pass SYNOICheckShareExt()
synocheckshare: Pass SYNOICheckServiceLink()
synocheckshare: Pass SYNOICheckAutoDecrypt()
synocheckshare: Pass SYNOIServiceShareEnableDefaultDS()
DiskStation> spacetool --synoblock-enum
****** Syno-Block of /dev/sda ******
//I've removed the output. This should display info about each disk in your array
DiskStation> vgchange -ay
# logical volume(s) in volume group "vg1" now active
DiskStation> dd if=/dev/vg1/syno_vg_reserved_area of=/root/reserved_area.img
24576+0 records in
24576+0 records out
DiskStation> synospace --map_file -d
Success to dump space info into '/etc/space,/tmp/space'
DiskStation> synocheckshare
synocheckshare: Pass SYNOICheckShare()
synocheckshare: Pass SYNOICheckShareExt()
synocheckshare: Pass SYNOICheckServiceLink()
synocheckshare: Pass SYNOICheckAutoDecrypt()
synocheckshare: Pass SYNOIServiceShareEnableDefaultDS()
DiskStation> synocheckiscsitrg
synocheckiscsitrg: Not Pass, # conflict
DiskStation> synocheckiscsitrg
synocheckiscsitrg: Pass