RAID5 Frequently Asked Questions

Various Questions

What disks are best used in a RAID5?

It is better to use the disks which are listed as compatible at the controller or NAS vendor site. If you cannot buy compatible disks for some reason, take any others. Some people think that it is better to use RAID Edition disks, Nearline SAS, and similar special models. In practice, any purchase of disks which are not in the compatibility list is a lottery. A little long in the tooth example is a Seagate Barracuda ATA IV hard drive which provided horrible performance in RAID, typically working slower than a single drive would do. This was eventually corrected by Seagate and for some time circa 2001 two versions of the drive were sold, one for desktop and the other for RAID use. More modern example, again from Seagate, is Barracuda ES.2 requiring reflash to work with certain Adaptec RAID controllers.

Why the capacity of the RAID 5 is less than I expected? What's up?

This can be due to the following:

• parity overhead;
• use of MBR instead of GPT to create partitions on the RAID. MBR only allows to create volumes with the size less than 2 TB.