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Top Ten RAID Tips

By Elena P

RAID, a Redundant Array of Inexpensive Disks, is the storage technology which becomes more and more widespread these days. Those who are planning to build a new RAID system would probably find the tips below useful.

1. Understand your requirements.

• Whatever your capacity requirements are, these are underestimated by the factor of two.
• Whatever the projected lifetime of the storage system is, it is underestimated.

2. The relationship between Speed, Price, and Fault Tolerance determines the RAID level to use. Of these three parameters, pick any two.

• Fast and Fault Tolerant - RAID 1+0.
• Fast and Cheap - RAID 0.
• Cheap and Fault Tolerant - RAID 5 or RAID 6.

3. If you are planning to build a RAID 0, consider using an SSD instead. Depending on what your requirements are, you may find a better bang for your buck with an SSD.

4. Hot spares are a good addition to a fault-tolerant array. If a drive has failed in a fault-tolerant (RAID 1 or RAID 5) array, there is a vulnerability window. If another drive fails during this vulnerability window, the data is lost. Hot spare drives allow the controller to rebuild the array without administrator intervention, thereby reducing the vulnerability window. The need for hot spare increases as the number of disks in array increases.

5. If you plan on building RAID 5 with a total capacity of more than 10 TB, consider RAID 6 instead. The probability of data loss during rebuild in a RAID 5 increases with the array size. RAID 6 does not have this problem.

6. Do not underestimate the software RAID. Do not use cheap controllers, use software RAID instead. The software RAID provides more reliability than entry-level server hardware RAID. It is also easier to move around from server to server.

7. Test fault tolerance and do it early. When deploying a fault-tolerant array (RAID 1, RAID 5, or RAID 6), test the system with a simulated disk failure. Just disconnect one of the disks with the system powered off. Do this before loading the array with the production data.

8. Even if your RAID is supposed to be fault tolerant, backup often. Although the RAID is redundant with respect to hard drive failures, there are correlated failures and many other issues that may bring down the entire arrays.

9. Monitor the RAID performance. Regularly check the SMART status on the drives using the appropriate software. Also, sudden unexplained drop in the throughput likely indicates a problem with one of the hard drives.

10. Recover a failed RAID. If there is a controller failure or an operator error, you might end up with a set of disks lacking the array configuration. You can then send the disk set to the data recovery lab, or try to get the data off yourself using ReclaiMe Free RAID Recovery.

Elena P. of ReclaiMe Free RAID Recovery

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