Chapter 7. Volumes 247
7.1.5  Striped and sequential volumes
The type attribute of a volume defines the method of allocation of extents that make up the 
volume copy:
/SM590000A striped volume contains a volume copy that has extents that are allocated from multiple 
MDisks from the storage pool. By default, extents are allocated by using round-robin 
algorithm from all MDisks in the storage pool. However, it is possible to supply a list of 
MDisks to use for volume creation.
Figure 7-5   Striped extent allocation
/SM590000A sequential volume contains a volume copy that has extents allocated sequentially on 
one MDisk.
/SM590000Image-mode volume is a special type of volume that has a direct one-to-one mapping to 
one (image mode) MDisk. 
For striped volumes, the extents are allocated from the set of MDisks (by default, all MDisks in 
the storage pool):
/SM590000An MDisk is picked by using a pseudo-random algorithm and an extent is allocated from 
this MDisk. This approach minimizes the probability of triggering the striping effect, which 
might lead to poor performance for workloads that generate many metadata I/O, or that 
create multiple sequential streams.
/SM590000All subsequent extents (if required) are allocated from the MDisk set by using round-robin 
algorithm.
/SM590000If an MDisk has no free extents when its turn arrives, the algorithm moves to the next 
MDisk in the set that has a free extent.
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 sufficient free space is available to create a striped volume copy, 
select one of the following options:
/SM590000Check the free space on each MDisk in the storage pool by using the lsfreeextents 
command.
/SM590000Allow the system to automatically create the volume copy by not supplying a specific 
stripe set.