M Values

RAID levels determine the values of M. Dynamic RAID reconstruction only changes the value of N. Table 2-1 describes M values for disk redundancy.

Number of RAID Columns

For disk redundancy, the number of RAID columns (N+M) is calculated as follows:

• RAID 5
  • For OceanStor Dorado 3000 V6, Number of RAID columns = Min (Number of member disks in a storage pool – Number of reserved columns, 15)
  • For OceanStor Dorado 5000 V6/OceanStor Dorado 6000 V6/OceanStor Dorado 8000 V6/OceanStor Dorado 18000 V6, Number of RAID columns = Min (Number of member disks in a storage pool – Number of reserved columns, 12)
• RAID 6 or RAID-TP: Number of RAID columns = Min (Number of member disks in a storage pool – Number of reserved columns, 25)

Wherein, Number of reserved columns = Max (1, Number of hot spare disks)

The methods for calculating the number of RAID columns in the following three scenarios are slightly different:

• On OceanStor Dorado 5000 V6/OceanStor Dorado 6000 V6, a storage pool spans over multiple controller enclosures and contains disks from smart disk enclosures.
• On OceanStor Dorado 8000 V6/OceanStor Dorado 18000 V6, eight controllers are configured without back-end full interconnection, and a storage pool spans over multiple controller enclosures.
• A storage pool with a single controller enclosure is expanded to span over multiple controller enclosures.

Number of member disks in a storage pool in the preceding formulas refers to the number of disks owned by a single controller enclosure for a storage pool.

Example:

For RAID 6 or RAID-TP:

Number of RAID columns = Min [Number of disks owned by a single controller enclosure for a storage pool – Number of reserved columns/2 (rounded up), 25]

Number of reserved columns = Max (1, Number of hot spare disks)

Example

A storage pool consists of 25 disks with RAID 6 (default value) and a hot spare policy of Low (1 disk). The number of RAID columns is calculated as follows:

Number of reserved columns = Max (1, Number of hot spare disks) = 1

Number of RAID columns = Min (Number of member disks in a storage pool – Number of reserved columns, 25) = Min (25 – 1, 25) = 24

The number of RAID columns (N+M) is 24 in this example.

RAID Usage

RAID usage = [(Number of RAID columns – Number of RAID parity columns M)/Number of RAID columns] x 100%

Example

The number of RAID columns (N+M) from the previous example is 24. The RAID level is RAID 6, so M is 2. RAID usage is therefore calculated as follows:

RAID usage = [(Number of RAID columns – Number of RAID parity columns M)/Number of RAID columns] x 100% = [(24 - 2)/24] x 100% = 91.67%

The RAID usage is 91.67%.