HP-UX Logical Volume Manager and MirrorDisk/UX Release Notes (September 2007)

Compatibility Issues
This release is specific for HP-UX 11i v3 (B.11.31). The following compatibility issues exist in the
February 2007 release of HP-UX 11i v3, as well as the September 2007 release.
Moving from HP-UX 11i v2 to HP-UX 11i v3
If you are migrating a system from HP-UX 11i v2 to HP-UX 11i v3, please refer to the LVM
migration white paper described in the “Related Documentation” section. It contains information
on migrating an LVM configuration from the legacy naming model to the agile naming model.
Existing LVM configurations created on HP-UX 11i v2 continue to work on HP-UX 11i v3 under
the legacy naming model. However, there is a change in behavior:
• Alternate Links (PVLinks): In HP-UX 11i v3, management of multi-pathed devices is
available outside of LVM using the next generation mass storage stack. By default, the next
generation mass storage stack distributes I/O requests across all available paths to a
multi-pathed disk, even when using legacy device special files. Using LVM with persistent
or legacy device special files may cause I/O requests to be sent across alternate links, even
if the links are not configured as PVLinks; this should not introduce any errors, but it does
differ from PVLink behavior in previous releases.
HP recommends converting volume groups with multi-pathed disks to persistent device
special files and native multi-pathing, as described in the migration white paper in “Related
Documentation”.
However, if you want backward-compatible PVLink behavior, you must use legacy device
special files for physical volumes, and disable the mass storage stack multi-pathing for those
physical volumes. To disable multi-pathing on legacy device special files, use the scsimgr
command to configure a global device tunable called leg_mpath_enable.
For each multi-pathed disk, enter the following command:
# scsimgr save_attr -D /dev/rdisk/diskn -a leg_mpath_enable=false
Alternatively, you can disable multi-pathing for all legacy device files with this command:
# scsimgr save_attr -a leg_mpath_enable=false
Note that this has no effect on multi-pathing through persistent device special files. For more
information, see scsimgr(1M).
Moving Volume Groups from HP-UX 11i v3 to Previous HP-UX Releases
If a volume group used on HP-UX 11i v3 is accessed from a system running a previous release
of HP-UX 11i, you may encounter these compatibility issues:
• Logical volumes larger than 2 TB: Releases prior to HP-UX 11i v3 can only access data
within the first 2 TB of a logical volume. If a logical volume larger than 2 TB is created on
HP-UX 11i v3, its use is not recommended on any previous HP-UX release. The volume
group can be activated and the logical volume can be used, but any data in that logical
volume beyond 2 TB will be inaccessible.
• Striped Mirrors: Releases prior to HP-UX 11i v3 only support extent-based striping via the
-D option to lvcreate. If a logical volume using simultaneous mirroring and
non-extent-based striping is created on HP-UX 11i v3, attempts to import or activate its
associated volume group will fail on a previous HP-UX release. To import the volume group,
you must remove the incompatible logical volumes or reduce them to a single mirror.
• Mirror Write Cache (MWC): When a volume group containing a logical volume using the
Mirror Write Cache is activated on HP-UX 11i v3, its Mirror Write Cache format is converted
to a new format. Importing or activating the volume group on a previous HP-UX release
does not recognize the new format and triggers a full resynchronization of the mirrors.
Compatibility Issues 9