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Why you shouldn't use normal HDDs with RAID 5

It is quite common to have a secondary storage unit for critical data such as important documents, photos, etc. While it is a solution to save sensitive information, it is a problem if the drive fails, the information could be lost. That's where RAID configurations come in, allowing you to make backup copies of this critical data. Among these is the RAID 5 configuration, highly recommended for fault tolerance.

It is true that RAID 5 configurations, despite high performance and fault tolerance, are repudiated by many. For professional use, other more robust solutions are recommended, being a bad decision to create a RAID 5 configuration. To improve the persistence of the data, the much more secure RAID 6 configurations are recommended.

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What is a RAID 5 configuration?

They are a division of data that is distributed in blocks with a parity system among the disks that are members of the set. This configuration has gained popularity due to the low cost of redundancy, being implemented with hardware support for parity calculation. At least 3 hard drives are required for these types of configurations and a maximum of 16 drives is recommended.

Theoretically the maximum number of drives in a RAID 5 can be unlimited

The data is spread across all drives and a parity checksum of all blocks is written to one drive. This parity data is not written to one drive, it is spread across all drives. Using the parity data the system can 'regenerate' the lost data into an information block.

Thus, RAID 5 configurations support only the failure of a single storage unit without losing data. This type of configuration can be done using software, although it is recommended to do it using hardware. Typically the additional cache of hardware support for configuration can improve performance.

Normally it is recommended to use hard drives of different batch, in case there is some kind of failure. Mixing units from different manufacturers is not recommended, as there could be large differences in performance.


RAID 5 configurations problems

One of the problems with RAID 5 configurations is that a portion of the hard drive's capacity cannot be used. Parity is saved across all drives, reducing the total capacity of our hard drives.

Another problem with RAID 5 is that when subjected to a workload of many writes smaller than the size of a strip, they present performance problems. This problem is due to the fact that the parity has to be updated on each write. It involves having to perform read, modify and write sequences in the data block and in the parity block.

On the other hand, when a disk fails, we must replace the unit and through array redundancy the unit must be rebuilt. This requires reading every bit of data from the rest of the drives without failures. For conventional SATA drives (not models designed for NAS) they have an unrecoverable Read Error Rate (URE) of once every 10 to the 14 (10e + 14) reads. Thus, during the matrix reconstruction process with conventional hard drives, the appearance of a URE is VERY likely.

When a URE is generated, the RAID controller will detect that a second drive has failed and the entire array will fail. As a result, ALL data in the RAID 5 configuration will be lost.


Alternatives to RAID 5

The RAID 5 configuration is widely used in the professional segment, although for the home segment it is taking too many risks. In data centers it is often used with a large number of disks, which confers reliability. For the home user, who will have few units, this configuration is not optimal since it carries the risk of losing all the information. The best options are:


RAID 10

This configuration is highly valued within the storage industry. We have a mirrored RAID 0 array which can be two or three way and always requires at least 4 drives. These types of configurations generally offer better performance and lower latency than other RAID systems with the exception of the RAID 0 configuration. This configuration is recommended when performing a large amount of data reads and writes.

It is also called RAID 1 + 0, or RAID 1 & 0

RAID 6

Expand RAID 5 configurations by adding an additional block of parity. Divide the data into blocks and distribute the two parity blocks among all members of the set. This configuration was not among the original RAID levels.

RAID 6 configurations may or may not have hot spare. They are created in order to resist the possible failure of two units, adding much more security. When using two drives per parity there is a penalty for performance, capacity, and the number of disks required.

configuration-raid-6
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Conclusion

In case of problems with the simple parity of the RAID 5 configuration we will lose all the information. The RAID 10 configuration is more recommended when the storage unit is used intensively. The RAID 6 configuration, meanwhile, is more recommended when working with sensitive information. Its dual parity unit configuration reduces the probability of catastrophic failure.


References

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Marco Antonio Ramirez

Computer Systems Engineer. I love video games and technology. My greatest achievement in life has been being the father of two beautiful daughters. Allergic to tuna and heaters.

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