Most used standard RAID levels explained:
- RAID 0 (stripped volume) – the data is split across two or more disks without parity, redundancy or fault tolerance. RAID 0 provide high performance, but if one drive fails the whole array is lost.
- RAID 1 (mirror volume) – the data is mirrored (exact copy) on two or more disks. If one drive fails, the array will continue to operate with only one member running.
- RAID 5 (stripped with parity) – this RAID will have 1 disk for parity and in case one drive will fail, the array will run but you will need to replace the disk right away and rebuild the array. If a second drive will fail, before the array is rebuild then the array will be lost.
- RAID 6 (stripped with double parity) – this RAID will have 2 disks for parity. In case one drive will fail you’ll still have a second drive for parity and the array will run even with two drives fail, but will be lost if a third drive fail.
Nested most used RAID levels explained:
- RAID 10 (RAID 1 + 0) – first is created RAID 1 and with a similar RAID 1 you create a RAID 0 by combining those two RAID 1 setups. Minimum for RAID 10 is four drives.
- RAID 50 (RAID 5+0) – first is created RAID 5 and with a similar RAID 5 you create a RAID 0 by combining those two RAID 5 setups. Minimum for RAID 50 is six drives (three for each RAID 5).
- RAID 60 (RAID 6+0) – first is created RAID 6 and with a similar RAID 6 you create a RAID 0 by combining those two RAID 6 setups. Minimum for RAID 60 is eight drives (four for each RAID 6).
OBS: The RAID is no substitute for Backups. No matter what RAID you have, you’ll still need Backups.
Creating the RAID – every RAID controller have different menus for creating the RAID and have defined RAID levels built-in that you cannot change. Some RAID controllers have only RAID 0, 1, 10. Other RAID controllers have RAID 0, 1, 5, 6, 10, 50, 60. When you buy a RAID controller make sure what RAID you want to create and make sure that controller have an option for that level. If this example, my RAID controller had only RAID 0, 1, 10 options. Every controller has a different key combination to go into the setup menu, you will see the option when the server boots up (most common key combinations are: Ctrl + C, Ctrl + R, Ctrl + I, Ctrl + E). My current RAID controller has the combination of Ctrl + C.
- Once you got into the menu you have the option to create the RAID 0, 1 or 10. In this case I’ve use the RAID 10.
- The next step is to choose which drives will create the array. You need to change “RAID Disk” from No to Yes. If you leave it No, then will not be added to this setup and the drive will not count for the total amount of space (see “Volume Size”, that will change every time when you change a disk from No to Yes). You can leave no drives, or you can leave one drive and set it up as a Hot Spare (the Hot Spare is a drive that is active and in standby for use if one of the drives fail. When a disk fails, data on the disk is rebuilt automatically on the hot spare disk in background)
- When you are Done with selecting the drive, press “C”. On the next window choose “Save changes then exit this menu”.
- On the next page you will see the whole array with all the disks included. The task that runs in background is to Initialize the RAID, for right now still shows “0%”. Click on “Manage Volume” to check the options.
- On the next page you can manage Hot Spares, check consistency of the array (check for errors), activate volume or delete the array.
- Since I’ve used all the drives to create this array I don’t have any drives available for Hot Spare. If you leave a drive to act as a Hot Spare, you will see it when you click on “Manage Hot Spares”. If you have any slots available to add another drive, you can add another one and use it as a Hot Spare. You need to change the Hot Spare from No to Yes for the drive that you choose to use it as a Hot Spare.
- If you want to delete the array, to create a different level, just choose “Delete Volume” and press “Y” to confirm.
- When is no RAID created, when the server boot up you will see all the drives available with the RAID controller at the top of the drives.
- After the RAID is created you will see only the Volume with the size for that array. The controller will also show at the top, before the Volume / Size.
