Chapter 6. Volume configuration 289
The
type attribute of a volume defines the allocation of extents that make up the volume copy:
A striped volume contains a volume copy that has one extent allocated in turn from each
MDisk that is in the storage pool. This is the default option, but you can also supply a list of
MDisks to use as the stripe set as shown in Figure 6-1.
Figure 6-1 Striped extent allocation
A sequential volume contains a volume copy that has extents that are allocated
sequentially on one MDisk.
Image-mode volumes are a special type of volume that have a direct relationship with one
MDisk.
6.1.1 Image mode volumes
Image mode volumes are used to migrate LUNs that were previously mapped directly to host
servers over to the control of the IBM Spectrum Virtualize system. Image mode provides a
one-to-one mapping between the logical block addresses (LBAs) between a volume and an
MDisk. Image mode volumes have a minimum size of one block (512 bytes) and always
occupy at least one extent.
An image mode MDisk is mapped to one, and only one, image mode volume.
The volume capacity that is specified must be equal to the size of the image mode MDisk.
When you create an image mode volume, the specified MDisk must be in unmanaged mode
and must not be a member of a storage pool. The MDisk is made a member of the specified
storage pool (Storage Pool_IMG_xxx) as a result of creating the image mode volume.
Attention: By default, striped volume copies are striped across all MDisks in the
storage pool. If some of the MDisks are smaller than others, the extents on the smaller
MDisks are used up before the larger MDisks run out of extents. Manually specifying
the stripe set in this case might result in the volume copy not being created.
If you are unsure if there is sufficient free space to create a striped volume copy, select
one of the following options:
Check the free space on each MDisk in the storage pool by using the lsfreeextents
command.
Let the system automatically create the volume copy by not supplying a specific
stripe set.
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