Hardware manual

Group Administration Group members
6–5
The RAID policy for a member consists of two parts:
• RAID level – RAID 10, RAID 50, RAID 5, or RAID 6. See RAID level characteristics.
Recommendation: For optimal performance, Dell recommends
that you assign the same RAID level to pool
members with the same disk type and disk speed.
• Spare drive policy – Whether the member automatically c
onfigures and uses spare disk drives. Spare drives
increase availability.
The number of spare drives depends on the array model and the number of installed drives. For RAID 6
Accelerated, o
nly one hard disk drive is configured as a spare. The solid-state drives are not protected by
sparing.
Recommendation: De
ll recommends that you use a spare-drive RAID policy. Only use a no-spare-drive
RAID policy if you have sufficient support staff and maintain a stock of replacement disk
drives.
The storage in the member is available after you set the RAID policy.
The member automatically configures the
disk drives according to the designated RAID level, with the appropriate number of spare drives.
Although all RAID levels provide good performance and data protection, ther
e are some differences. When
choosing a RAID policy, you should identify the performance and availability needs of your workload and select a
RAID policy that meets those needs. If your workload has mixed requirements in terms of performance and
availability, you might want to consider mixing RAID levels in a multi-member group.
RAID level characteristics
The characteristics of each supported RAID level are:
• RAID 10 – Striping on top of multiple RAID 1 (mirrored) sets.
•
RAID 50 – Striping on top of multiple RAID
5 (distributed parity) sets.
• RAID 5 – One or more RAID 5 sets.
• RAID 6 – One or more RAID 6 (dual parity) sets.
RAID 6 Accelerated is supported only on array mo
dels with disk drive configurations that include both solid-
state drives and hard disk drives. RAID 6 Accelerated optimizes the use of solid-state drives for critical data.
One hard disk drive is configured as a spare and provides redundancy protection in the event of a hard disk
drive failure or a solid-state disk drive failure.
Each RAID 1 set or RAID 5 set can survive a single disk drive
failure. A RAID
6 set can survive two simultaneous
drive failures. If a drive fails in a RAID set, the RAID set is degraded.
Consider the following performance and availa
bility factors when choosing a RAID level for a member:
• RAID 10 and RAID 50 provide excellent reliability for your dat
a, in addition to overall high performance.
• RAID 10 provides the best performance for workloads
that are mostly small random writes.
• RAID 6 provides high availability, but at the expense of performance during data reconstruction.
• RAID 6 is not recommended for workloads consis
ting mainly of random writes.