Administrator Guide

Adding virtual disk groups
The system supports a maximum of two pools, one per controller module: A and B. You can add up to 16 virtual disk groups for each virtual
pool. If a virtual pool does not exist, the system will automatically add it when creating the disk group. Once a virtual pool and disk group
exist, volumes can be added to the pool. Once you add a virtual disk group, you cannot modify it. If your organization's needs change, you
can modify your storage amount by adding new virtual disk groups or deleting existing ones.
Depending on the type of disks selected, virtual disk groups belong to one of the following tiers:
• Enterprise SAS disks: Standard tier.
• Midline SAS disks: Archive tier.
• SSDs: Performance tier.
NOTE: All virtual groups in the same tier within a virtual pool should have the same data protection level to provide
consistent performance across the tier.
NOTE: If a virtual pool contains a single virtual disk group, and it has been quarantined, you cannot add a new virtual
disk group to the pool until you have removed the existing disk group from quarantine. For information about removing a
disk group from quarantine, see the Dell EMC PowerVault ME4 Series Storage System CLI Guide .
Adding linear disk groups
The system supports a maximum of 64 pools and disk groups. Whenever you add a linear disk group, you also automatically add a new
linear pool. You cannot add further disk groups to a linear pool. However, you can expand storage by adding disks and dedicated spares to
existing linear disk groups.
All of the disks in a linear disk group must share the same classification, which is determined by disk type, size, and speed. This provides
consistent performance for the data being accessed on that disk group. When you delete a linear disk group, the contained volumes are
automatically deleted. The disks that compose that linear disk group are then available to be used for other purposes.
Read-cache disk groups
If your system has SSDs, you can also add read-cache disk groups. Read cache is a special type of virtual disk group that can be added
only to a virtual pool. It is used for the purpose of caching virtual pages for improving read performance. A virtual pool can contain only one
read-cache disk group. A virtual pool cannot contain both read cache and a Performance tier. At least one virtual disk group must exist
before a read-cache disk group can be added. NRAID is automatically used for a read-cache disk group with a single disk. RAID-0 is
automatically used for a read-cache disk group with the maximum of two disks. When you create a read-cache disk group, the system
automatically creates a read-cache tier, if one does not already exist. Unlike the other tiers, it is not used in tiered migration of data.
Disk group options
The following options appear in the top section of the Add Disk Group panel:
Table 16. Disk group options
Option Description
Name A disk group name is case-sensitive and can have a maximum of 32 bytes. The name
cannot already exist in the system or include the following: " , < \
Type When creating a disk group, select one following:
• Virtual: Shows options for a virtual disk group
• Linear: Shows options for a linear disk group
• Read Cache: Shows options for a read cache disk group
Pool (only appears for virtual and read-
cache disk groups)
Select the name of the virtual pool (A or B) to contain the group.
Assign to (optional, only appears for linear
disk groups)
For a system operating in Active-Active ULP mode, this option specifies the controller
module to own the group. To let the system automatically load-balance groups between
controller modules, select the Auto setting instead of Controller A or Controller B.
Working in the Pools topic 81