Administrator Guide

Table 3. Number of disks per RAID level to optimize virtual disk group performance (continued)

RAID level Number of disks (data and parity)

6 4 total (2 data disks, 2 parity disks); 6 total (4 data disks, 2 parity

disks); 10 total (8 data disks, 2 parity disks)

10 4–16 total

ADAPT 12–128 total

Table 4. Linear disk group expansion by RAID level

RAID level Expansion capability Maximum disks

NRAID Cannot expand. 1

0, 3, 5, 6 You can add from 1 to 4 disks at a time. 16

1 Cannot expand. 2

10 You can add 2 or 4 disks at a time. 16

50 You can add one sub-group at a time. The

added sub-group must contain the same

number of disks as each of the existing sub-

groups.

ADAPT You can add up to 68 disks at a time. 128

About ADAPT

ADAPT is a RAID-based data protection level that maximizes flexibility, provides built in spare capacity, and allows for very fast rebuilds,

large storage pools, and simplified expansion. All disks in the ADAPT disk group must be the same type (enterprise SAS, for example), and

in the same tier, but can have different capacities. ADAPT is shown as a RAID level in the management interfaces.

ADAPT disk groups use all available space to maintain fault tolerance, and data is spread evenly across all of the disks. When new data is

added, new disks are added, or the system recognizes that data is not distributed across disks in a balanced way, it moves the data to

maintain balance across the disk group.

Reserving spare capacity for ADAPT disk groups is automatic since disk space dedicated to sparing is spread across all disks in the system.

In the case of a disk failure, data will be moved to many disks in the disk group, allowing for quick rebuilds and minimal disruption to I/O.

The system will automatically default to a target spare capacity that is the sum of the largest two disks in the disk group, which is large

enough to fully recover fault tolerance after loss of any two disks in the disk group. The actual spare capacity value can change depending

on the current available spare capacity in the disk group. Spare capacity is determined by the system as disks are added to a disk group, or

when disk groups are created, expanded, or rebalanced. For more information, see the topic about the add disk-group command in

the Dell EMC PowerVault ME4 Series Storage System CLI Guide.

ADAPT disk groups can be expanded to either replenish current target spare capacity or to increase usable capacity. For more information,

see Expanding a disk group on page 84.

A system using ADAPT disk groups cannot be downgraded to a system that does not support ADAPT.

About SSDs

The use of SSDs (solid-state drives) can greatly enhance the performance of a system. Since the SSDs do not have moving parts, data

that is random in nature can be accessed much faster. You can use SSDs for virtual disk groups. When combined with virtual disk groups

that consist of other classes of disks, improved read and write performance is possible through automated tiered storage. Alternatively,

you can use one or two SSDs in read-cache disk groups to increase read performance for pools without a Performance tier. The

application workload of a system determines the percentage of SSDs of the total disk capacity that is needed for best performance.

For more information about automated tiered storage, see About automated tiered storage on page 23. For more information on read-

cache disk groups, see Read-cache disk groups on page 15. For information about using SSDs in all disk groups, see All-flash array on page

19.

Getting started