On Mon, 11 Jan 2016 09:54:42 +1300, Ian Stewart wrote:
Scenario 1: Using console terminal commands I remove disk_3 USB stick from the mirror-set and take it to another computer. Can it be mounted and read as single JOBD or must it be mounted as a single unit of a mirror set in order to be read?
You mean JBOD? That should work if you mount it read-only. I would avoid trying to write to it, or you could corrupt the RAID metadata. I was effectively doing this sort of thing with older versions of GRUB, by setting it to boot off one of the members of the RAID container.
Scenario 2: At the command line I remove disk_3 USB stick from the mirror set. Can I then mount this disk on this same computer as a single JOBD or must it be as a single member of another mirror-set? E.g. So that I could do a network based backup of disk_3 while the other two disks in the mirror-set continue their normal operations.
Again, it should work if you mount it read-only. Also, note that you don’t need to remove it from the array in order to make direct accesses to it on the same machine. It still remains available under its original device name. I take advantage of this for doing badblocks scans on disks. If you are doing backups, I would do them at the file level. You can reduce the impact on the system with ionice(1).
Scenario 3: Without using commands to elegantly remove disk_3 from the mirror-set, I just pull out disk_3 USB stick. I continue writing data to the remaining mirror-set. One hour later I plug back in disk_3. Will it auto-magically be joined to the existing mirror-set and updated so it contains current data? ...OR, do I need to enter commands to get it to be rejoined to the existing mirror-set?
Can’t recall encountering this actual situation (all the cases where disks disappeared from the array were due to crashes). But I’m pretty sure if it doesn’t get picked up automatically, you can re-add it manually.
Scenario 4: Without using commands to elegantly remove disk_3 from the mirror-set, I just pull out disk_3 USB stick. I then plug in disk_4 USB stick. Will disk_4 be auto-magically joined to the existing mirror-set and updated? ...OR do I need to enter commands?
Same situation as scenario 3. There are commands if needed to do this manually.