Les Mikesell wrote:
Can you add a mirror to any LVM after creating it without making provisions ahead of time as you must when setting up raid devices?
Not sure how the lvm2 implementation in linux is, as I have not seen any docs for how it is supposed to work. In AIX, you do it on the fly with mklvcopy and you can make up to two copies (so 3 in total, one "original" and two copies) and you remove it with rmlvcopy. This can be done on the fly regardless of filesystem or if it is mounted or not since it all occurs at LVM leven and below the filesystem.
I have found it useful to create 'broken raid' devices that could be mirrored on demand to external drives and have been thinking about doing it over iscsi too. However it doesn't seem possible to install the system on a raid with missing devices.
Yes, this is a use for the feature. Kind of a simple snapshot where you can make a portable copy of a filesystem (after the copy, you split off the PV from the VG).