Introduction to RAID : RAID Levels : RAID 60

RAID 60

RAID 60 provides the features of both RAID 0 and RAID 6, and includes both parity and disk striping across multiple drive groups. RAID 6 supports two independent parity blocks per stripe. A RAID 60 virtual drive can survive the loss of two drives in each of the RAID 6 sets without losing data. RAID 60 is best implemented on two RAID 6 drive groups with data striped across both drive groups.

RAID 60 breaks up data into smaller blocks and then stripes the blocks of data to each RAID 6 disk set. RAID 6 breaks up data into smaller blocks, calculates parity by performing an exclusive-or on the blocks, and then writes the blocks of data and parity to each drive in the drive group. The size of each block is determined by the stripe size parameter, which is set during the creation of the RAID set.

RAID 60 can support up to 8 spans and tolerate up to 16 drive failures, though less than total drive capacity is available. Two drive failures can be tolerated in each RAID 6 level drive group.

Table 13. RAID 60 Overview

Uses

Provides a high level of data protection through the use of a second parity block in each stripe. Use RAID 60 for data that requires a very high level of protection from loss.

In the case of a failure of one drive or two drives in a RAID set in a virtual drive, the Nytro MegaRAID controller uses the parity blocks to re-create all of the missing information. If two drives in a RAID 6 set in a RAID 60 virtual drive fail, two drive rebuilds are required, one for each drive. These rebuilds can occur at the same time.

Use for office automation and online customer service that requires fault tolerance. Use for any application that has high read request rates but low write request rates.

Strong points

Provides data redundancy, high read rates, and good performance in most environments. Each RAID 6 set can survive the loss of two drives or the loss of a drive while another drive is being rebuilt. Provides the highest level of protection against drive failures of all of the RAID levels. Read performance is similar to that of RAID 50, though random reads in RAID 60 might be slightly faster because data is spread across at least one more disk in each RAID 6 set.

Weak points

Not well suited to tasks requiring lot of writes. A RAID 60 virtual drive has to generate two sets of parity data for each write operation, which results in a significant decrease in performance during writes. Drive performance is reduced during a drive rebuild. Environments with few processes do not perform as well because the RAID overhead is not offset by the performance gains in handling simultaneous processes. RAID 6 costs more because of the extra capacity required by using two parity blocks per stripe.

Drives

A minimum of 8.

The following figure shows a RAID 60 data layout. The second set of parity drives is denoted by Q. The P drives follow the RAID 5 parity scheme.

Figure 17. RAID 60 Level Virtual Drive