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RAID 6: A comparison with RAID 5

Jasmine Desai, Principal Correspondent

RAID (Redundant Arrays of Independent Disks) has its own place in the storage arena, especially with storage

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as a concept taking off quite seriously in India. There are half a dozen RAID levels which organizations can choose from; the more persistent one seems to be RAID 5. With criticality and protection of data becoming more vital with each passing day, RAID 6 is slowly making its way into the storage infrastructure of Indian organizations.

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The pros and cons

The main question that arises: Why should organizations shift to RAID 6 leaving their comfort zone of a certain RAID level? Also, for which organizations does it make sense? To find the answer, one needs to take a close look at the advantages of RAID 6 as well as its downside.

The biggest advantage is its ability for dual disk parity. Explains Niket Trivedi, Storage Engineer, Visa International, Singapore, "Currently, some hard disk drives (HDDs) have a capacity of almost 1 TB, in contrast to HDD capacities just a decade ago which were not over 30 GB. Thus, the amount of time needed to fix the fail drive would be more, and it would be a smarter decision to have dual disk failure protection." RAID 5 seems to work really fine with SMBs, which are cost-conscious and do not have any great need to extra protect their data, though in certain environments it may be otherwise.

Apart from the additional protection, RAID 6 provides high fault tolerance, thus sustaining simultaneous disk failures. According to Aman Munglani, Principal Analyst, Gartner India, "It is a safer option given that in today's environment there are a lot of organizations having SATA-based drives which are extremely huge in terms of capacity but low on reliability." Thus, RAID 6 is more valid when there is a large capacity to address. SATA is less reliable than SCSI drives or FC drives, hence when environments need added security, RAID 6 makes a lot of sense.

On the downside, one would need to buy a lot more in terms of raw disk space. It will cost more upfront due to the additional drive that needs to be procured. As two of the disk drives are being used for parity, the dilemma is between raw disk space and usable space.

Also, for RAID 6, one needs a more complex system with a method for encoding. One also needs hardware acceleration, otherwise the performance suffers. Thus, performance loss is one more disadvantage. Says Pritam Pawar, Storage Consultant, Network Techlab, "Nowadays we get intelligent raid controllers which enhance the performance. SSD drives from different vendors provide high IOPS, which reduce theperformance impact for RAID 6."

Should you opt for it?

Although security of data is a top priority for most organizations, it is not necessary to jump on the RAID 6 bandwagon. Organizations should move from RAID 5 to RAID 6 only if they feel that their business uptime is more critical. Remarks Trivedi, "Personally, I would stick to RAID 5 rather than go in for RAID 6 because the former will always perform better and faster. But any particular application needing uptime with low disk performance should be sitting in a RAID 6 configuration. Please note that RAID 5 is faster than RAID 6."

The main pre-requisite to be a RAID 6 organization is the existence of data that requires high availability and high protection.

There are certain recommended configurations for RAID 6 that one can go for. According to Pawar, "The number of disks one should use for a raid array should be a minimum of four drives. Second, the stripe size setting should be according to the data requirement (OLTP/database)."

Trivedi adds, "It depends on the expected performance versus how much risk we are allowed to take." Hardware suppliers of storage should perform a test for individual customers with their performance requirements and configure accordingly.

The Indian scene 

Is India on a RAID 6 ride or will it always go side-by-side with other RAID levels? According to Srinivas Rao, Director, Presales & Solutions, Hitachi Data Systems, "A lot of customers are going for RAID 6 because the density of disk drives has gone up, and the chances of losing data in case of a disk failure in the RAID 5 configuration are more. RAID 6 is mostly deployed on Serial ATA because the density there is more."

Storage vendors are now offering the RAID 6 feature in their storage boxes; this might pick up aggressively since virtualization and cloud computing are fast catching up among Indian organizations.

Comments Munglani, "A lot of Indian organizations are already adopting RAID 6. Extremely tech-savvy companies are more on the RAID 6 vine. However, even organizations with Fibre Channel drives with mission-critical applications have started implementing it."

Thus, it's not a question of competition between RAID 5 and RAID 6. One can always put mission-critical data on RAID 6 and let the rest of it reside on the former. There will be no real need to shift completely from RAID 5 to RAID 6. With data security becoming vital even for SMBs, RAID 6 will slowly go hand in hand with its forerunner.