Using Serviceguard Extension for RAC, 10th Edition, April 2013

ASM over SLVM
SGeRAC support for ASM-over-SLVM continues in HPUX 11i v3. SGeRAC 11.17.01 or later is
required for ASM-over-SLVM configurations on HP-UX 11i v3.
NOTE: For additional information about integrating ASM over SLVM configuration in SGeRAC
cluster environment, see “SGeRAC Toolkit for Oracle RAC 10gR2 or later” (page 102)
The advantages of the "ASM-over-SLVM" configuration are as follows:
• ASM-over-SLVM ensures that the HP-UX devices used for disk group members will have the
same names (the names of logical volumes in SLVM volume groups) on all nodes, easing ASM
configuration.
• ASM-over-SLVM protects ASM data against inadvertent overwrites from nodes inside/outside
the cluster. If the ASM disk group members are raw disks, there is no protection currently
preventing these disks from being incorporated into VxVM volume/disk groups.
The disadvantages of the ASM-over-SLVM configuration are as follows:
• Additional configuration and management tasks are imposed by the extra layer of volume
management (administration of volume groups, logical volumes, physical volumes).
• There is a small performance impact from the extra layer of volume management.
• SLVM has some restrictions in the area of online reconfiguration, the impact of which will be
examined later in this chapter.
Configuring SLVM Volume Groups for ASM Disk Groups
We would like the logical volumes presented to ASM to resemble raw disks, as far as possible.
Hence, each SLVM logical volume (LV) used as a member of an ASM disk group is required to be
laid out to occupy the usable space, in contiguous fashion, of exactly one single physical volume
(PV). This implies the following about LV:
• Contiguous
• Not be striped or mirrored
• Does not span multiple PVs
• Does not share a PV with other LVs
The idea is that ASM provides the mirroring, striping, slicing, and dicing functionality as needed
and SLVM supplies the multipathing functionality not provided by ASM. Figure 14 indicates this
1-1 mapping between SLVM PVs and LVs used as ASM disk group members.
Further, the default retry behavior of SLVM could result in an I/O operation on an SLVM LV taking
an indefinitely long period of time. This behavior could impede ASM retry and rebalance
capabilities; hence a finite timeout must be configured for each SLVM LV. For example, the timeout
could be configured to the value (total number of physical paths to the PV * PV timeout), providing
enough time for SLVM to try all available paths, if needed.
The PVs used in an ASM disk group can be organized into SLVM volume groups as desired by
the customer. In the example shown in Figure 14, for each ASM disk group, the PVs corresponding
to its members are organized into a separate SLVM volume group.
SGeRAC Support for ASM on HP-UX 11i v3 97