RAID stands for Redundant Array of Individual Disks. For a full explanation check the Wikipedia page here.
There many different levels of RAID and the descriptions below cover the RAID levels most commonly used by LILIN Servers and =.
RAID 0 is the RAID level usually used for speed and performance when reading and writing to HDD’s. This RAID level does not offer any redundancy usually associated with RAID, if anything it removes redundancy completely from the system. Data being saved to the systems HDD’s is split across multiple HDD’s allowing the system to write and read from multiple drives giving faster read and write times to the system. If one HDD fails within the system, you will lose all the data on all the HDD’s.
RAID 1 is a mirror configuration. This level of RAID offers a high level of redundancy but is not a very efficient and cost effective use of HDD storage. Each single HDD must have a counterpart HDD installed and data is written to both HDD’s simultaneously. If one HDD fails a replacement HDD can be fitted and the data will be copied from the remaining working HDD to the new HDD to bring the redundancy feature back to the unit.
RAID 5 offers both redundancy and a cost effective level of storage. In a RAID 5 configuration you must use at least 3 HDD’s, however the system will only see 2 HDD’s as visible storage, the other HDD is used as a parity HDD allowing for 1 disk failure within the system. If a HDD fails in a RAID 5 configuration this HDD must be swapped for a working HDD of the same size as the original HDD. The unit will then offer the ability to restore the information on the failed HDD using the information on the remaining HDD’s. With RAID 5 if you experience 2 HDD failures concurrently you will lose all the information across all the active HDD’s.
RAID 5 + Spare
This configuration must use at least 4 HDD’s. RAID 5 + Spare will still only give the visible storage of 2 HDD’s as the 3rd HDD is still a parity drive, however the 4th HDD is kept as a spare. If a HDD failure is detected the spare HDD will automatically kick in and the unit will automatically recover the data using the 2 remains HDD’s and the spare. It is then advisable to swap the failed HDD for a new disk. This will then become the spare HDD for any future HDD failure. RAID 5 + Spare will offer the best redundancy when using the NVR1400 & NVR2400 units.
RAID 6 offers a more resilient redundancy than RAID 5. In a RAID 6 configuration you must use at least 4 HDD’s, however the system will only see 2 HDD’s as visible storage. The other HDD’s are used as parity HDD’s allowing for 1 disk failure within the system. If a HDD fails in a RAID 6 configuration this HDD must be swapped for a working HDD of the same size as the original HDD. The unit will then offer the ability to restore the information on the failed HDD using the information on the remaining HDD’s. With RAID 6 if you experience 2 HDD failures concurrently you will lose all the information across all the active HDD’s.
RAID 6 offers more advantages over RAID 5 when a drive failure occurs. RAID 6 has 2 parity HDD's to recover the failed HDD information from rather than just 1. The issue with having only 1 parity hdd to rebuild a failed HDD from is that if the remaining parity HDD has an issue E.G. a bad sector, this can compromise the rebuild ability of the failed HDD meaning this may not be possible. This in turn means the entire RAID array will need to be rebuilt meaning all information could be lost unless the surviving information is archived to a different location until the RAID array is reconfigured.