An Explanation of RAID Levels [u]

[ This article was first published in the July, 2009, issue of Larry Jordan’s Edit Smarter Newsletter.  Updated August, 2014, and July, 2017 (for SSDs). Updated Dec. 11, 2022, with better wording. Updated Dec. 20, 2024, with two real-world charts.]

RAIDs (Redundant Array of Independent Disks/Drives/Devices) consist of a number of hard drives or SSDs grouped together into a single unit so that they appear to the computer as a single device. Because there is more than one hard drive in a RAID, they offer greater performance and storage.

There are different levels of RAIDs, identified by numbers:

RAID 0 – EXTREMELY fast, no data redundancy. Requires a minimum of two hard drives inside the RAID enclosure. The more drives you add, the faster the performance, as performance and storage capacity are the sum of all drives in the RAID. However, if you lose one drive, you’ve lost ALL your data. Most often used when speed combined with low cost are paramount. This also provides the maximum storage capacity of a RAID.

RAID 1 – VERY slow, total data redundancy. Generally only uses two hard drives inside the RAID enclosure. Often called “mirroring,” each drive is a complete copy of the other. Most often used for backing up servers or when on-set for DIT media work. Has the speed and capacity of the slowest single drive in the system. This provides the storage capacity of a single drive in the RAID.

RAID 3 – Medium-fast, data redundancy. This technology is no longer in common use, replaced by the faster performance of RAID 4 or 5 systems.

RAID 4 – Very fast, data redundancy. Requires a minimum of three drives, as one drive is reserved solely for parity data. Should one drive die, your data is safe. This is the preferred RAID format for SSD drives because of how the data is stored on the drives. This reduces total storage capacity by the amount of one drive in the RAID.

RAID 5 – Very fast, data redundancy. Requires a minimum of three drives and shares parity data across all drives. Most often found with four or more drives inside. If one drive goes down, your data is safe. This is the preferred format for RAIDs containing spinning media (traditional hard disks). Used for both locally-attached storage and servers. This reduces total storage capacity by the amount of one drive in the RAID.

RAID 6 – Fast, extra data redundancy. Requires a minimum of four drives. This version protects your data in the event two hard drives die at the same time. More expensive than RAID 5, but, generally, the same physical size. Like RAID 5 this is most often used connected to just one computer. Not as fast as a RAID 5. This reduces total storage capacity by the amount of two drives in the RAID.

RAID 10 (or 1+0) – Fast, total data redundancy. Requires a minimum of four drives, this is more often created by combining two matched RAID 0’s into a RAID 1. This provides the speed equivalent of a RAID 0, with the data redundancy of RAID 1. As RAIDs continue to drop in price, this can be a less-expensive way to create systems that rival the performance of a RAID 50. This reduces total storage capacity by 50%.

RAID 50 – VERY fast, data redundancy. Generally the domain of very large RAIDs, this format combines the speed of RAID 0 with the redundancy of RAID 5 by dividing the RAID into sections, where you can lose a drive in each section without losing data. These systems generally cost more than $10,000 and contain at least twelve drives. Generally used in network and server situations where multiple users need to access the same data.

RAID 60 – Fast, extra data redundancy. Generally the domain of very large RAIDs, this format combines the speed of RAID 0 with the redundancy of RAID 6 by dividing the RAID into sections, where you can lose two drives in each section without losing data. These systems generally cost more than $10,000 and contain at least twelve drives. Generally used in network and server situations where multiple users need to access the same data.

The most popular RAID formats are: 0, 1, and 5. The following charts are based on real-world tests using an OWC Thunderbay 4 four-drive HDD RAID and an OWC ThunderBlade NVMe SSD RAID, formatted using SoftRAID and connected via Thunderbolt 3.

This chart shows real-world speed differences between the most popular HDD RAID types. RAID 0 is best for speed, while RAID 5 is recommended in case of hardware failure. Personally, I recommend RAID 5 for HDD RAIDs.

This chart shows real-world speed differences between the most popular SSD RAID types. RAID 0 is best for speed, while RAID 4 is recommended in case of hardware failure. Personally, I recommend RAID 0 for SSD RAIDs due to the hardware reliability of SSDs, coupled with daily backups.

EXTRA CREDIT

• This PDF describes my HDD test results and testing procedure.
• This PDF describes my SSD test results and testing procedure.