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RAID 6 vs. RAID 10

There are numerous RAID configurations to choose from, but navigating the nuances of each can take a lot of work. In the case of RAID 6 and 10, both have distinct pros and cons.

Deciding when to use RAID 6 vs. RAID 10 is an issue that gives many storage administrators trouble. While RAID...

5 is the most-used type of RAID, the benefits of different levels suit different uses.

RAID 6 and RAID 10 can be used as alternatives to RAID 5, depending on the priorities of the organization. Preventing data loss, meeting performance requirements and maximizing capacity are some of the factors that should be taken into consideration when deciding on a RAID level.

RAID stands for redundant array of independent disks, and it comes in a wide range of configurations. RAID 10 -- also known as RAID 1+0 -- is a nested RAID level, combining the benefits of RAID 1 and RAID 0. RAID 10 mirrors the data, then stripes the result across the disks.

RAID 6 is a standard RAID level. It stripes the data and calculates parity twice, with the results stored in different blocks on the disks. Both RAID 6 and RAID 10 provide fault tolerance, which can offer some peace of mind when it comes to potential data loss.

To better compare these two RAID levels, we'll take a look at the advantages of each.

RAID 6 uses less storage

A RAID 10 array can only store half of its total disk capacity in data, as the other half is used by the mirror. If a RAID 6 array contains the minimum number of disks -- four -- then it can only hold half the total disk capacity in data, as well, because RAID 6 reserves the capacity amount of two drives to hold parity. The difference comes as you add disks.

A RAID 10 array dedicates half its capacity to protection no matter how many disks are used. But the percentage of usable capacity increases as you add disks to a RAID 6 array. If you use eight disks in RAID 6, for example, parity -- still the equivalent to two drives -- only consumes 25% of the disk capacity.

RAID 6 is more compute-intensive

Because RAID 6 requires two parity calculations for each write operation, it writes slower than most other RAID levels. RAID controller coprocessors are often employed to handle parity calculations and to improve RAID 6 write speed.

RAID 6 can protect against two disk failures

The major weakness of RAID 6 is that it takes a long time to rebuild the array after a disk failure.

Because RAID 6 uses a double parity scheme, it can protect against the simultaneous failure of two disks. RAID 10 may or may not be able to protect against two disk failures depending on where they occur.

If both failed disks are in the same mirror, then the other mirror can take over. If the disks in both mirrors fail, you have a problem.

RAID 10 is faster to rebuild

The major weakness of RAID 6 is that it takes a long time to rebuild the array after a disk failure because of RAID 6's slow write times. With even a moderate-sized array, rebuild times can stretch to 24 hours, depending on how many disks are in the array and the capacity of the disks. Because RAID 6 users tend to use the largest capacity disks they can afford, this is an increasingly serious limitation for RAID 6.

RAID 10 doesn't require special hardware

Most controllers support RAID 10 with good performance. If you are going to use RAID 6, it is important to use a controller specifically designed to support it. RAID 6 essentially doubles the parity calculations for every write.

RAID 6 vs. RAID 10: Which should you choose?

The RAID configuration you choose often depends on what kind of storage you're protecting and how much capacity is required. RAID 6 is mostly found in installations using SATA drives, especially large-capacity SATA disk drives.

There's no technical reason why you can't use RAID 6 with SCSI drives, but there's not much incentive to do so. SCSI drives are generally smaller than SATA drives and they are considered to be more reliable.

As a nested RAID level, RAID 10 provides the benefits of two reliable RAID configurations. RAID 10 is one of the few RAID levels optimized for use with SSDs, so as the price of flash continues to drop, RAID 10 is an appealing option to combine with a flash environment.

When deciding which RAID array to use, you should consider budget, capacity, read/write speeds and rebuild/recovery time.

Next Steps

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