RAID 1 Minimum Drive Requirements Explained
RAID 1 is one of the safest RAID levels you can have, and yet it doesn’t require lots of hard disks to set up. This RAID configuration offers the highest redundancy and fault tolerance. But then, it is one of the slowest RAID levels in terms of performance; so, when choosing RAID 1, you have to consider if performance and “bigger” storage space are a core requirement for your setup, or if you’re just interested in having high business availability probability and fault tolerance.
What is RAID 1?
RAID 1 is simply referred to as “Disk Mirroring.” It is a RAID storage technique where data is mirrored in its block form across all disks used in the array so that all the RAID drives will have uniform data. In RAID 1 storage, you’re only getting the total storage capacity of one of the drives in the array; this is because all drives in the array will contain the same data, mirrored.
This RAID configuration is not relatively fast since data is mirrored in its original (bulk) size across all the disks and read in the same manner. However, because of the disk mirroring feature, RAID 1 is the most reliable RAID configuration with the highest fault tolerance you can get from a RAID storage. A RAID 1 level will continue to function and be accessible even if multiple drives fail in the array – you just need only one active drive in the array to keep the RAID alive.
But, before you set up this RAID level, it is important that you have considered and compared other “faster” and “high-performance” RAID levels such as RAID 5 and RAID 10. Notwithstanding, RAID 1 is one of the cheapest RAIDs to configure because it doesn’t require many disks for the minimum configuration.
Note: The essential purpose of setting up RAID 1 is for data redundancy and data protection, especially in environments where high availability and fault tolerance are needed for the systems.
How RAID 1 Works
As mentioned earlier, this RAID level uses a data storage technique known as disk mirroring. This technique means that, if you have four (4) hard disks on your RAID 1 array, when data is written to the RAID storage, the data is received by the first disk in the RAID. It gets mirrored (in its exact format and content) across the remaining three (3) disks in the RAID 1 array. So, all four disks in the RAID array will contain the same data, in the same format.
Since all the disks in a RAID 1 contain the same data sets, the array can survive multiple simultaneous drive failures until the last drive fails too, then the RAID becomes inaccessible. As per our example, it means that a RAID 1 with four drives will continue to function even if three (3) drives in the array have failed. All your files and data on the RAID 1 will continue to be accessible from the last surviving drive; you will only lose everything if this last drive fails too.
Hence, the moment your RAID 1 surfers from multiple drive failures already, make sure to replace those failed drives; don’t wait until there’s only one good drive remaining. This high data reliability of RAID 1 makes it an ideal choice for environments where data protection and redundancy are needed.
However, it is important to note that RAID 1 offers low storage space. For example, if you set up RAID 1 with four (4) hard drives of 1 TB space each, instead of getting 4 TB of storage space (or 3.8 TB, logically), what you will get is just 1 TB of free space. This is because, all the drives will be saving the same data volumes, so when one of them gets filled up, the rest will be filled too, For this reason, it is best to use drives of the same space for RAID 1 setups, because if you use a smaller hard drive along with bigger ones, the RAID will offer you a total storage capacity equivalent to the storage capacity of the smaller drive – once that smaller drive gets filled with data, your entire RAID storage gets full, irrespective of whether there’s still space on the bigger capacity drives.
Minimum Number of Drives for RAID 1
Unlike most other popular RAID levels, the minimum number of drives for RAID 1 is two (2) hard disks; it could be HDDs or SSDs, but preferably SSDs because of the several advantages they offer ahead of traditional HDDs. You need at least two disks in RAID 1 because the RAID will have to mirror data from the first disk to the second disk for redundancy purposes. But, a RAID 1 with only 2 drives may fail easily, which is why 4-drive setups are usually the best-advised option, to allow for higher data protection even if 2 drives fail at once.
Why Two Drives are Essential
RAID is defined as the Redundant Array of Independent Disks, with emphasis on “disks.” You cannot have a RAID with a single drive, there has to be a minimum of two drives, even so, RAID levels like RAID 5, RAID 6, and RAID 10 require a minimum of 3 – 4 drives to set up.
But in RAID 1, which is our focus, the use of two drives is essential so that when one of the drives fails, the RAID can read from the remaining good drive, while you replace the other failed one and rebuild. If you have a 2-drive RAID 1, it is important to rebuild RAID array immediately after you notice that one of the drives has failed, so you don’t risk losing all your data the moment the second drive probably fails, too.
Can RAID 1 Use More Than Two Drives?
Yes, you can have 4-drive or even 6-drive RAID 1, but this is not usually advised because you’d be spending a lot of money and still not get “more” storage space. RAID 1 only offers the storage of one (1) drive in the array as the total storage of the RAID. This means, that even if you have a 6-drive (2 TB SSDs x 6) RAID 1, what you’re getting as the total storage is just 2TB space, which is the capacity of just one of the drives.
So, instead of spending so much on hard disks and not necessarily getting more space, it is best to buy high-capacity disks (5 TB – 10 TB disks) and have a 2-drive or 4-drive RAID 1. Also, the more drives in your RAID 1, the slower the write performance as the RAID would need to write datasets in blocks to all the drives, every time. Better still, if you want a multi-drive RAID setup with high redundancy, you should consider a RAID 10.
Comparing RAID 1 to Other RAID Levels
RAID 1 isn’t the only good and reliable RAID level out there; there are other impressive – and even faster – RAID levels, which include RAID 0, RAID 5, and RAID 6. However, RAID 0, RAID 5, and RAID 6 use a technique known as “Data Striping,” although in different ways.
- RAID 0: This RAID level is the fastest among all RAID levels. It uses data striping with zero parity, which means that if the RAID suffers only one drive failure, the entire RAID fails along with the drive, and your data stored on the RAID becomes inaccessible and lost. But, data striping on RAID 0 means that data is striped into bits as it gets written into the RAID, and those smaller data bits get distributed uniquely across all the member drives in the RAID array, such that each disk drive contains a different data bit from the other. This method allows for faster read and write performance but with zero parity!
- RAID 5: This RAID level follows the same pattern with RAID 0, but integrates a dedicated parity drive, which allows the RAID to survive only one drive failure. If more than one drive fails simultaneously in a RAID 5, the entire RAID will go down.
- RAID 6: This RAID level follows the route of RAID 5, but this time, it uses dual parity drives, which allows it to survive a maximum of two simultaneous drive failures. If more than 2 drives fail at once or simultaneously, the RAID will go down.
How does RAID 1 stack up against these RAID levels? You need a minimum of three (3) hard disks for the RAID setup; and a minimum of four (4) hard disks for the RAID 6 basic setup; and even though you can use only two drives for RAID 0, the RAID 0 array has no parity or redundancy, so the chances of losing your entire RAID data to one single drive failure is high.
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When to Choose RAID 1 Over Other Configurations for Personal and Enterprise Use
Everyone’s data storage choices and needs differ, but here are some common scenarios where RAID 1 could prove to be a better option than any other level of RAID.
- When high availability and near-zero downtime are required for your business applications and servers.
- Home media server setups where data protection is more important than speed and performance.
- Enterprise data centers and database environments where redundancy is highly required for workstations.
Conclusion
RAID 1 is one of the most popular RAID choices, thanks to its data mirroring capabilities and high redundancy. But then, it’s not among the fastest RAID levels in terms of speed and performance. So, this RAID level is best for environments where data reliability and protection are cherished over speed and performance. More so, it is affordable to set up, only requires a minimum of two drives, and you can set it up as software or hardware RAID using any external controller.