Administrator Guide

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.

Linear disk groups

A linear disk group requires the specification of a set of disks, RAID level, disk group type, and a name. Whenever the system creates a

linear disk group, it also creates an identically named linear pool at the same time. No further disk groups can be added to a linear pool.

For maximum performance, 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. To dissolve a linear disk group, delete

the disk group and the contained volumes are automatically deleted. The disks that compose that linear disk group are then available to be

used for other purposes.

The RAID levels for linear disk groups created through the PowerVault Manager must be fault tolerant. The supported RAID levels for

linear disk groups in the interface are: RAID 1, RAID 5, RAID 6, RAID 10, RAID 50 and ADAPT. RAID 10 and RAID 50 only appear in the

interface if the system's disk configuration supports them. If RAID 10 is specified, the disk group has a minimum of two sub-groups. If

RAID 50 is selected, depending on the number of selected disks, varying numbers of sub-groups can be created. Additionally, you can

create fault-tolerant RAID-3 or non-fault-tolerant NRAID or RAID-0 disk groups through the CLI.

NOTE: Tiering, snapshots, and replications are not available for linear pools.

Read-cache disk groups

A read-cache disk group is a special type of a virtual disk group that is used to cache virtual pages to improve read performance. Read

cache does not add to the overall capacity of the pool to which it has been added. You can add or remove it from the pool without any

adverse effect on the volumes and their data for the pool, other than to impact the read-access performance.

If your system uses SSDs, you can create read-cache disk groups for virtual pools if you do not have any virtual disk groups for the pool

that are comprised of SSDs. Virtual pools cannot contain both read-cache and a Performance tier.

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