AIX Version 4.3 Differences Guide

• Concurrent mode volume groups
• Filesystem and database access
Note that filesystem access does not mean JFS access. This enhancement to the
LVM still requires additional steps (such as unmounting a file system) to prevent
data loss.
This new feature is used for HACMP concurrent mode (mode 3). While in
concurrent mode, you can designate a mirror copy in a VG as a backup copy to
archive the data on the raw logical volume without affecting the other mirror
copies. It improves the system availability to end users.
Use a second LV and special device to allow access to the backup mirror copy.
All I/O and ioctls coming to this second LV would be routed to the actual logical
volume to be serviced. A number of changes were made to VGDA to support this
new type of LV.
If the LV contains a filesystem, there will be two serial writes to support the new
mountpoint. In order to support this function, there are updates to the LVCB and
the superblock of the new filesystem.
5.7.1 Limitations
Following are some limitations:
• The original logical volume cannot be removed while the on-line backup copy
exists. No changes are allowed to the original logical volume structure, or
attributes, while the on-line backup exists. But you still can make changes to
the filesystem mounted over the logical volume.
• All partitions of a logical volume must be fresh before you mark a mirror copy
as an on-line backup. Only one copy may be designated as an on-line backup
copy.
• This function is currently documented only in the man pages. Use at your own
risk.
5.7.2 Commands Changed
Using the chlvcopy command, you can mark, or unmark, a mirror copy as an
on-line backup copy and change the backup mirror copy characteristics for a
logical volume.
The syntax is:
chlvcopy -B | { -b [ -c copy ] [ -f ] [ -P ] [ -l newlvname ] [ -w ] } LV name
Logical Volume Manager Enhancements 93