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Comparison of nine Serial ATA RAID 5 adapters

RAID 6 and RAID 50 performance

Besides RAID 0, 1, 5 and 10, a number of the adapters in this review are also supporting RAID 6 and 50. The boards supporting RAID 50 are the 3ware Escalade 9500S-8, the LSI MegaRAID SATA 150-6 and the RAIDCore 4852. RAID 6 is an unique feature of the Areca ARC-1120. The performance in RAID level 6 and 50 will be briefly discussed on this page. We won't repeat the endless benchmark graphs seen on the previous pages of this article.

As implied by its name, RAID 50 is a combination of RAID 5 (block-level striping with distributed parity) and RAID 0 (block-level striping). A RAID 50-array is therefore a stripe of two or more RAID 5 arrays. Some RAID adapters are limited a two stripes, others have the ability to stripe more than two RAID 5 arrays. The minimum number of hard disks for a RAID 50 array is two times the minimal number in RAID 5, therefore six disks. A configuration with six drives will loose the capacity of two drives due to storage of parity information. The advantage of RAID 50 lies in its higher fault tolerance: two hard disks are allowed to fail in a RAID 50 array, but only one disk may fail in each individual RAID 5 array. The functioning of RAID 6 is equal to that of RAID 5, however in this case parity is stored twice, resulting in the loss of effective capacity from two drives. RAID 6 offers a higher fault tolerance than RAID 50: two drives may fail at all time, irrespective of their position in the array.

In theory, RAID 50 promises increased write performance over RAID 5. The results of our write STR benchmarks demonstrate that none of the adapters is capable of improving write performance in RAID 50. Random I/O performance improved significanly on the 3ware Escalade 9500S-8 and the LSI MegaRAID SATA 150-6. RAID 6 offers no performance advantage, which is completely logical since there is one less stripe available compared to a RAID 5 array consisting of an equal number of drives. The RAID 50 configurations where tested using six disks so the MegaRAID SATA 150-6 (having only six ports) could be included in this comparison. RAID 6 on the Areca ARC-1120 was tested with eight hard disks because the need for double parity is best felt at the highest number of disks.

With the exception of the 3ware Escalade 9500S-8, the performance of all adapters was negatively influenced by the use of RAID 6 and RAID 50. The RAIDCore BC4852 and the LSI MegaRAID SATA 150-6 only suffered a small performance degradation in RAID 50, though. For this reason, RAID 50 is certainly worth considering if higher fault tolerance is desired and a lower effective capacity is no issue. The performance of RAID 6 on the Areca ARC-1120 RAID 6 was considerably lower than RAID 5 on this card.

In our server benchmark the 3ware Escalade 9500S-8 produces a considerable performance profit if used in RAID 50. The difference with the six disks RAID 5-setup is no less than 26 per cent. At the RAIDCore BC4852 we see a small decrease in the performances, but this time the MegaRAID is a little bit faster in the server benchmarks than it was in RAID 5. Again the Areca ARC-1120 performed considerably less than it did in RAID 5.


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