## 6.3.2 RAID level 

The DS8000 series offers RAID 6, RAID 10, and RAID 5. By default, the DS Storage Manager GUI suggests a configuration with RAID 6. 

## RAID 6 

RAID 6 increases data fault tolerance. It can tolerate two disk failures in the same rank, as compared to RAID 5, which is single disk fault tolerant. RAID 6 uses a second independent distributed parity scheme (dual parity). RAID 6 provides a read performance that is similar to RAID 5, but RAID 6 has a larger write penalty than RAID 5 because it must calculate and write a second parity stripe. 

Consider RAID 6 in situations where you might consider RAID 5, but need increased reliability. RAID 6 was designed for protection during longer rebuild times on larger capacity drives to cope with the risk of a second drive failure within a rank during rebuild. RAID 6 has the following characteristics: 

GLYPH<SM590000> Sequential Read: About 99% x RAID 5 rate 

GLYPH<SM590000> Sequential Write: About 65% x RAID 5 rate 

GLYPH<SM590000> Random 4 K 70% R /30% W IOPS: About 55% x RAID 5 rate 

If two drives fail in the same rank, the performance degrades during the rebuild. 

Important:  Configure large-capacity drives as RAID 6 arrays. RAID 6 is advised as the default for all drive sizes now. 

## RAID 10 

A workload that consists of mainly random writes , which is usually the case when you have a higher write ratio, benefits from RAID 10. Here, data is striped across several disks and mirrored to another set of disks. A write causes only two disk operations when compared to four operations of RAID 5, or six of RAID 6. 

RAID 10 requires nearly twice as many drives (and twice the cost) for the same capacity when compared to RAID 5, but it can achieve four times greater random write throughput. 

Therefore, it is definitely worth considering the use of RAID 10 for high-performance random write workloads. 

Tip:  Consider RAID 10 for random-write ratios over 35%. Note that RAID 10 is not supported with the 7.68 TB (and larger) Flash Tier 2 drives. 

The decision to configure capacity as RAID 10, RAID 6, or (for small drives) RAID 5, and the amount of capacity to configure for each type, can be made at any time. RAID 6, RAID 5, and RAID 10 arrays can be intermixed within a single system. In addition, the physical capacity can be logically reconfigured later (for example, RAID 6 arrays can be reconfigured into RAID 10 arrays). However, the arrays must first be emptied. Changing the RAID level is not permitted when logical volumes exist. 

With flash drives, due to their high amount of possible I/Os per second per array, the need for a RAID 10 is often not as pending anymore as it was for spinning disk drives. 

## RAID 5 

RAID 5 has often been used because it provides good performance for random and sequential workloads, and it does not need much more storage for redundancy (one parity drive). The DS8000 series can detect sequential workload. When a complete stripe is in 

