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245Creating volumes
Creating a volume on specific disks
Specifying ordered allocation of storage to volumes
Ordered allocation gives you complete control of space allocation. It requires
that the number of disks that you specify to the
vxassist command must match
the number of disks that are required to create a volume. The order in which you
specify the disks to
vxassist is also significant.
If you specify the
-o ordered option to vxassist when creating a volume, any
storage that you also specify is allocated in the following order:
1 Concatenate disks.
2 Form columns.
3 Form mirrors.
For example, the following command creates a mirrored-stripe volume with 3
columns and 2 mirrors on 6 disks in the disk group, mydg:
# vxassist -b -g mydg -o ordered make mirstrvol 10g \
layout=mirror-stripe ncol=3 \
mydg01 mydg02 mydg03 mydg04 mydg05 mydg06
This command places columns 1, 2 and 3 of the first mirror on disks mydg01,
mydg02 and mydg03 respectively, and columns 1, 2 and 3 of the second mirror
on disks mydg04, mydg05 and mydg06 respectively. This arrangement is
illustrated in Figure 7-1.
Figure 7-1 Example of using ordered allocation to create a mirrored-stripe
volume
For layered volumes,
vxassist applies the same rules to allocate storage as for
non-layered volumes. For example, the following command creates a striped-
mirror volume with 2 columns:
# vxassist -b -g mydg -o ordered make strmirvol 10g \
layout=stripe-mirror ncol=2 mydg01 mydg02 mydg03 mydg04
This command mirrors column 1 across disks mydg01 and mydg03, and column
2 across disks mydg02 and mydg04, as illustrated in Figure 7-2.
Striped plex
Striped plex
Mirror
Mirrored-stripe
volume
Column 1 Column 2 Column 3
Column 1 Column 2 Column 3
mydg01-01 mydg02-01 mydg03-01
mydg04-01 mydg05-01 mydg06-01