When the need to evacuate all persistent SAN storage from EMC DMX1K to HP XP12K (HDS), three main solutions were envisaged. The first one was brute data copy (tar, cpio, etc.) but was not very practical with the size of the data (multi-terabytes) and the time involved in copying them. The two others were based on LVM technologies: mirroring, or moving.

Although the choice has been to use the online and transparent moving data technology (see pvmove for more information), it was interesting to note that Red Hat has backported support for the creation and manipulation of simple mirrors to their RHEL4 distribution. These functionalities were introduced with the RHBA-2006:0504-15 advisory issued on 2006-08-10, i.e. between RHEL4 Update 4 and RHEL4 Update 5 (and so available via RHN at this time). It is just too bad that the online help for LVM commands are not properly synchronized nor fully documented by the corresponding manual page: clearly, this doesn't help to use them in the best conditions (no, Google isn't always the better option when using these kinds of functionalities in big companies).