Hiya
I chickened out of trying to move my files around to accommodate the change in RAID so decided to start again and rebuild 
Has gone OK so far, although I should've deleted the RAID before wiping the physical drives, judging by the carnage that caused! Couldn't get OMV to boot until I ejected the drives first, then inserted one at a time so OMV could recognise them. Managed to find a command in CLI to clear the superblock info from the 2 original drives, which then allowed me to add them to my RAID5.
I've now finished creating the RAID5 (took about 6 hours) and my 4x3TB drives are showing a total capacity of 8.19TB, but now having issues with the file systems. I've created a new ext4 file system which is attributed to /dev/md0 - it says it's online but it's not mounted. Does the file system creation take hours to finish and I'm just trying to move things along too quickly? Any way to monitor if it's doing anything?
My original shared folders are present and I've updated the volume to point to md0 but they're not accessible yet, presumably because the file system isn't mounted?
If I try to mount I get an error:
Failed to mount 'f608fd07-91e0-4ef2-931d-525a287d093c': mount: no such partition found
Error #6000:
exception 'OMVException' with message 'Failed to mount 'f608fd07-91e0-4ef2-931d-525a287d093c': mount: no such partition found' in /usr/share/openmediavault/engined/rpc/filesystemmgmt.inc:887
Stack trace:
#0 [internal function]: OMVRpcServiceFileSystemMgmt->mount(Array, Array)
#1 /usr/share/php/openmediavault/rpcservice.inc(125): call_user_func_array(Array, Array)
#2 /usr/share/php/openmediavault/rpc.inc(79): OMVRpcServiceAbstract->callMethod('mount', Array, Array)
#3 /usr/sbin/omv-engined(501): OMVRpc::exec('FileSystemMgmt', 'mount', Array, Array, 1)
#4 {main}
I also still have my original file system (I presume) sitting with lots of n/a markings and status of 'missing' - is that an issue or can it be ignored? I'm assuming in CLI I could potentially clear this? There's no device marked and deleting it is greyed out.
ETA - another error I get if I try to apply config changes is:
File contains invalid JSON (filename=/var/lib/openmediavault/fstab_tasks.json):
Error #6000:
exception 'OMVException' with message 'File contains invalid JSON (filename=/var/lib/openmediavault/fstab_tasks.json): ' in /usr/share/php/openmediavault/util.inc:274
Stack trace:
#0 /usr/share/php/openmediavault/module.inc(141): OMVJsonFile->read()
#1 /usr/share/openmediavault/engined/module/fstab.inc(52): OMVModuleAbstract->execTasks('delete')
#2 /usr/share/openmediavault/engined/rpc/config.inc(164): OMVModuleFsTab->stopService()
#3 [internal function]: OMVRpcServiceConfig->applyChanges(Array, Array)
#4 /usr/share/php/openmediavault/rpcservice.inc(125): call_user_func_array(Array, Array)
#5 /usr/share/php/openmediavault/rpcservice.inc(158): OMVRpcServiceAbstract->callMethod('applyChanges', Array, Array)
#6 /usr/share/openmediavault/engined/rpc/config.inc(224): OMVRpcServiceAbstract->callMethodBg('applyChanges', Array, Array)
#7 [internal function]: OMVRpcServiceConfig->applyChangesBg(Array, Array)
#8 /usr/share/php/openmediavault/rpcservice.inc(125): call_user_func_array(Array, Array)
#9 /usr/share/php/openmediavault/rpc.inc(79): OMVRpcServiceAbstract->callMethod('applyChangesBg', Array, Array)
#10 /usr/sbin/omv-engined(501): OMVRpc::exec('Config', 'applyChangesBg', Array, Array, 1)
#11 {main}