8456ch_Perf.fm Draft Document for Review December 11, 2019 12:14 pm 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 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.  RAID 6 RAID 10 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  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. 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. 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. 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. 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.  Important:  Configure large-capacity drives as RAID 6 arrays. RAID 6 is advised as the  default for all drive sizes now. If two drives fail in the same rank, the performance degrades during the rebuild. 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 160  IBM DS8900F Architecture and Implementation