Restricted mappings
Many hosts are able to map up to 256 LUNs (0–255) per storage partition. However, the maximum number of mappings differs because of
operating system variables, multipath failover driver issues, and potential data problems. The hosts listed in the table have these mapping
restrictions.
If you try to map a virtual disk to a LUN that exceeds the restriction on these operating systems, the host is unable to access the virtual
disk.
Table 13. Highest lun of operating systems
Operating System
Highest LUN
Windows Server 2003 and Windows Server 2008
255
Linux
255
Guidelines when you work with host types with LUN mapping restrictions:
•
You cannot change a host adapter port to a restricted host type if there are already mappings in the storage partition that would
exceed the limit imposed by the restricted host type.
•
Consider the case of the Default Group that has access to LUNs up to 256 (0–255) and a restricted host type is added to the Default
Group. In this case, the host that is associated with the restricted host type is able to access virtual disks in the Default Group with
LUNs within its limits. For example, if the Default Group had two virtual disks mapped to LUNs 254 and 255, the host with the
restricted host type would not be able to access those two virtual disks.
•
If the Default Group has a restricted host type assigned and the storage partitions are disabled, you can map only a total of 32 LUNs.
Any additional virtual disks that are created are put in the Unidentified Mappings area. If more mappings are defined for one of these
Unidentified Mappings, the
Define Additional Mapping
dialog shows the LUN list, and the
Add
button is unavailable.
•
Do not configure dual mappings on a Windows host.
•
If there is a host with a restricted host type that is part of a specific storage partition, all the hosts in that storage partition are limited
to the maximum number of LUNs allowed by the restricted host type.
•
You cannot move a host with a restricted host type into a storage partition that already has LUNs mapped that are greater than what is
allowed by the restricted host type. For example, if you have a restricted host type that allows only LUNs up to 31, you cannot move
that restricted host type into a storage partition that has LUNs greater than 31 already mapped.
The Default Group on the
Host Mappings
tab has a default host type. To change the host type, right-click on the host and select
Change
Default Host Operating
System from the pop-up menu. If you set the default host type to a host type that is restricted, the maximum
number of LUNs allowed in the Default Group for any host is restricted to the limit imposed by the restricted host type. If a particular host
with a nonrestricted host type becomes part of a specific storage partition, you are able to change the mapping to a higher LUN.
Storage partitioning
A storage partition is a logical entity consisting of one or more virtual disks that can be accessed by a single host or shared among hosts
that are part of a host group. The first time you map a virtual disk to a specific host or host group, a storage partition is created.
Subsequent virtual disk mappings to that host or host group do not create another storage partition.
One storage partition is sufficient if:
•
Only one attached host accesses all the virtual disks in the storage array
•
All attached hosts share access to all the virtual disks in the storage array
When you choose this type of configuration, all the hosts must have the same operating system and special software (such as clustering
software) to manage virtual disk sharing and accessibility.
More than one storage partition is required if:
•
Specific hosts must access specific virtual disks in the storage array
88
Disk groups, standard virtual disks, and thin virtual disks
