The alternative is to use a host-based Logical Volume Manager (LVM) when the planned workloads
require either more space or IOPS capacity than the individual physical volumes can provide. LVM
is the disk management feature available on UNIX-based operating systems, including Linux, that
manages their logical volumes.
The following illustrates a fixed-size provisioning environment using LUNs in host-managed logical
volumes:
In either case, hosts recognize the size as fixed regardless of the actual used size. Therefore, it is
not necessary to expand the volume (LDEV) size in the future if the actual used size does not exceed
the fixed size.
When such a logical volume runs out of space or IOPS capacity, you can replace it with one that
was created with even more physical volumes then copy over all of the user data. In some cases,
it is best to add a second logical volume then manually relocate just part of the existing data to
redistribute the workload across two such volumes. These two logical volumes would be mapped
to the server using separate host paths.
Disadvantages
Some disadvantages to using fixed-sized provisioning are:
•
If you use only part of the entire capacity specified by an emulation type, the rest of the
capacity is wasted.
•
After creating fixed-sized volumes, typically some physical capacity will be wasted due to
being less than the fixed-size capacity.
•
In a fixed-sized environment, manual intervention can become a costly and tedious exercise
when a larger volume size is required.
14
Introduction to provisioning
