Dell PowerVault ME5 Series Administrator's Guide

ADAPT

ADAPT is a RAID-based data protection level that:

• Maximizes flexibility
• Provides built in spare capacity
• Optimizes performance
• Allows for very fast rebuilds, large storage pools, and simplified expansion

If a disk fails in an ADAPT disk group, and the failed disk is replaced with a new disk in the same slot, the replacement disk will be added to the disk group automatically. All disks in the ADAPT disk group must be the same type (enterprise SAS, for example), but can have different capacities, provided the range of difference does not exceed a factor of two. For example, mixing a 600 GB disk and a 1.2 TB disk is acceptable; but mixing a 6 TB disk and a 16 TB disk could prove problematic. It is conceivable that a sizeable difference between mixed disk capacities (ratio greater than two) could prevent consuming space on disks due to insufficient distributed space required to support striping.

All disks in an ADAPT disk group are used to hold user data, but not all disks will be used by each page of data. To increase fault tolerance, any available capacity on disks can be allocated as spare for reconstruction purposes. When new data is added, new disks are added, or the system recognizes that data is not distributed across disks in a balanced way, the system moves the data to maintain balance across the disk group.

Spare disks are not used by ADAPT disk groups since the RAID design provides built-in spare capacity that is spread across all disks in the disk group. In the case of a disk failure, data will be redistributed 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 ADAPT 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.

ADAPT disk groups can be expanded to either replenish current target spare capacity or to increase usable capacity. You can expand an ADAPT disk group from the Maintenance > Storage panel.

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