Which RAID level has the best price-to-performance comparison?


Which RAID level has the best price-to-performance comparison?

Antony Adshead, UK bureau chief, storage

RAID levels are arrived at by combining the following attributes: a) mirroring data between sets of drives; b) striping data across drives; c) striping mirror sets or mirroring striped sets; and d) using parity data to enable disk rebuilds. But a key aim of RAID is data protection, so if we take that goal into account as something we want to perform well, what are the price-to-performance comparisons of the various RAID configurations?

RAID 0: Best performance, poor data protection

In terms of raw price/performance, RAID 0 has the lowest cost. All disk space is used to store data; none is used for mirroring or parity data. Performance is good in terms of I/O, as data is striped across disks and there's no overhead created by parity calculations.

But RAID 0 offers the least data protection. If a disk fails, you'll have to accept the loss of that data or the drive being down while you restore it from other media.

RAID 1 and 10: Better data protection, but at a cost

RAID 1 offers excellent data protection by mirroring data between two identical sets of disks. Because of this duplication, you're immediately paying double for your useable capacity – if you have 4x 500 GB disks in a RAID 1 set, you'll only get 1 TB useable capacity, as half comprise the mirrored data. Also, RAID 1 doesn't stripe, so you'll lose out on performance compared to RAID 0.

By mirroring sets in a striped set of disks, RAID 10 gives the data protection of RAID 1 as well as the striping -- and therefore performance -- of RAID 0. However, as with RAID 1, you pay for twice as much raw capacity than you can actually use.

RAID 5: Best price, performance and data protection? 

RAID 5 stripes data and protects it by distributing parity data across all disks. Because no extra disks are occupied with mirroring, RAID 5 costs are immediately less than those for RAID 1 and its derivatives. Data protection is good because of parity enabling drive rebuilds, but performance takes a hit because of the processing overhead in calculating parity data.

Price-to-performance comparison results

While RAID 0 is the least costly, it could never be used for databases unless you can withstand data loss or rebuild adequately from other backed up media.

RAID 1 and 10 win on data protection, but lose in terms of disk costs. RAID 10 offers the best performance and data protection, but at a cost.

RAID 5 offers the best trade-off in terms of price and performance, and includes data protection for database use.

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