Administrator Guide

Some advantages of using virtual storage are:
● It allows performance to scale as the number of disks in the pool increases.
● It virtualizes physical storage, allowing volumes to share available resources in a highly efficient way.
● It allows a volume to be comprised of more than 16 disks.
Virtual storage provides the foundation for data-management features such as thin provisioning, automated tiered storage, SSD
read cache, and the quick rebuild feature.
The linear method maps logical host requests directly to physical storage. In some cases the mapping is one-to-one, while in
most cases the mapping is across groups of physical storage devices, or slices of them. This linear method of mapping is highly
efficient. The negative side of linear mapping is lack of flexibility. This makes it difficult to alter the physical layout after it is
established.
About disk groups
A disk group is an aggregation of disks of the same type, using a specific RAID level that is incorporated as a component of a
pool, for the purpose of storing volume data. Disk groups are used in both virtual and linear storage environments. You can add
virtual, linear, or read-cache disk groups to a pool.
NOTE: After you create a disk group using one storage type, the system will use that storage type for additional disk
groups. To switch to the other storage type, you must first remove all disk groups. For more information, see Removing disk
groups on page 88.
All disks in a disk group must be the same type SSD: enterprise SAS, or midline SAS, For example, a disk group can contain
different models of disks, and disks with different capacities and sector formats. If you mix disks with different capacities, the
smallest disk determines the logical capacity of all other disks in the disk group, for all RAID levels except ADAPT. For example,
the capacity of a disk group composed of one 500 GB disk and one 750 GB disk is equivalent to a disk group composed of two
500 GB disks. To maximize capacity, use disks of similar size.
Sector format
The system supports 512-byte native sector size disks, 512-byte emulated sector size disks, or a mix of these sector formats.
The system identifies the sector format used by a disk, disk group, or pool as follows:
● 512n—All disks use the 512-byte native sector size. Each logical block and physical block is 512 bytes.
● 512e—All disks use 512-byte emulated sector size. Each logical block is 512 bytes and each physical block is 4096 bytes.
Eight logical blocks will be stored sequentially in each physical block. Logical blocks may or may not be aligned with physical
block boundaries.
● Mixed—The disk group contains a mix of 512n and 512e disks. For consistent and predictable performance, do not mix disks
of different sector size types (512n, 512e).
You can provision storage by adding a disk group to a pool. Volumes then can be created in the pool.
Virtual disk groups
A virtual disk group requires the specification of a set of disks, RAID level, disk group type, pool target (A or B), and a name. If
the virtual pool does not exist at the time of adding the disk group, the system will automatically create it. Multiple disk groups
(up to 16) can be added to a single virtual pool.
NOTE:
For optimal performance all virtual disk groups in the same tier should have the same RAID level, capacity disks, and
physical number of disks.
When a virtual disk group is removed that contains active volume data, that volume data will drain or be moved to other
disk group members within the pool, if they exist. Disk groups should only be removed when all volume data can cleanly be
drained from the disk group. When the last disk group is removed, the pool ceases to exist and will be deleted from the system
automatically.
NOTE: If the last disk group contains data, a warning appears prompting you to confirm removing the disk group.
The RAID level for a virtual disk group must be fault tolerant. The supported RAID levels for virtual disk groups are: RAID 1, RAID
5, RAID 6, RAID 10, and ADAPT. If RAID 10 is specified, the disk group must have at least two sub-groups.
Getting started
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