HP NonStop G-Series - Manual (Page 58)

Configuring and Managing SMF Processes
HP NonStop Storage Management Foundation User's Guide—523562-008
3-8
Considerations for Data
Creating Partitioned Files On Virtual Disks
In a situation where all the partitions reside on the physical disks, there is a risk of
losing one partition in case one physical disk fails. This is not the case in a system that
has some partitions residing on physical disks and some on virtual disks.
When a partitioned file resides on a virtual disk, two scenarios are possible:

The primary partition is on a physical disk. Some of its secondary partitions reside
on physical disks and some reside on virtual disks.

The primary partition is on a virtual disk. Some of its secondary partitions reside on
physical disks and some reside on virtual disks.
In the first case only, there is a risk of losing more than one partition if a physical disk
fails. If a secondary partition on a physical disk and the physical file corresponding to a
secondary partition on a virtual disk happen to be on the same physical disk, and that
disk fails, two partitions will be lost. HP suggests that you do not place the physical file
(which corresponds to a secondary partition on a virtual disk) on a physical disk that
already has a secondary partition. Use the PHYSVOL option to place the physical file
on the appropriate physical disk.
The following example demonstrates this:
Assume that we have two virtual disks, $V1 and $V2 and two physical disks, $P1 and
$P2 in one SMF pool, $PP1. A file TEST.PART has its primary partition on $V1. Its
secondary partitions are
$V2.TEST.PART
$P1.TEST.PART
Also, assume that the physical file corresponding to the secondary partition
$V2.TEST.PART is $P1.ZYS00000.A00000M2. This means that the secondary
partition $P1.TSET.PART and the physical file corresponding to the secondary partition
$V2.TEST.PART are on the same physical disk, $P1. In case physical disk $P1 fails,
you would lose both of the secondary partitions. You should avoid this situation.
Use the PHYSVOL option to create secondary partition $V2.TEST.PART and place its
physical file on $P2 or use the FUP RELOCATE command to move the physical file
from $P1 to $P2.
Co-Location Of Data
Many users optimize applications by co-locating certain data files on the same disks or
by spreading data across multiple disks for maximum parallelism. Before moving an
application to SMF, you should understand how the application is currently tuned so
that optimization can be preserved. Co-location of data is preserved when a disk is
converted by using SMCONVRT. It can also be preserved when using RESTORE by
specifying the PHYSVOL option, which forces all the restored files to be located on the
same physical volume.