RAID Options Explained

RAID (Redundant Array of Independent Discs) adds resilience and reliability to a server, protecting its operating system and storage Hard Disc Drives (HDDs) against failure. There are seven levels of RAID. Usually, when VMS Co. provides a server with RAID, the Operating System is configured in RAID 1 (mirrored) on Solid State Drives (SSDs) for fast operation. The storage array is configured in RAID 5 on SATA HDDs, allowing each storage HDD to be hot-swapped (changed without stopping the server) with a replacement, if it fails, without losing any recorded video data.

The server Operating System is typically set up on either two 256GB or two 480Gb SSD’s configured as a RAID 1 pair. If one fails, the other drive already has a copy of all data, there is no perceptible disruption to server up time.

Typical Microsoft (Server 2022 or Windows 11) or Ubuntu Linux operating systems need no more than 256Gb to operate perfectly well. Our standard builds are 480Gb however, if the build is 256Gb due to availability, no compromise in performance will occur.

RAID 5 is applied to CCTV storage applications because it offers a strong balance between storage capacity and resilience. However, to implement the RAID 5 operation, the capacity equivalent to around 1.5 individual HDDs must be sacrificed to operate.

If one storage hard drive fails in a RAID 5 array it can be replaced with the same size and type of HDD whilst the server remains live and operational, without losing any data; known as Hot Swap. Provided the failed HDD is replaced promptly, the array will rebuild and return to normal operation.

As HDD capacity has increased, much larger RAID 5 storage volumes are possible. However, RAID 5 has storage volume limits dependent on the HDD partitioning and file system used, which must also be considered. An NTFS (New Technology File System)-formatted array, the primary system format used by Microsoft to store, organize, and manage files, such as RAID 5, has a 64 TB volume limit. This affects RAID 5 array sizes as follows:

Example 1 – 70TB RAID 5

A RAID 5 array storage volume comprising 7x 10TB HDDs delivers 70TB total RAW and 55TB in RAID 5 of usable storage.

15TB is lost to RAID 5 (1.5x GDDs) and the useable storage is within the 64TB limit.

Example 2 – 90 TB RAID 5

A RAID 5 array storage volume comprising 5x 18TB HDDs delivers 90TB total RAW and 63TB in RAID 5 of usable storage.

As the individual HDD capacity is 18TB, 27TB is lost to RAID 5, with the useable storage kept within the 64TB limit.

Example 3 - 140TB RAID 5

A RAID 5 storage volume comprising 14x 10TB HDDs delivers 140TB total RAW. However, the storage volume capacity limit means that instead of delivering 125TB RAID 5 (140TB less 1.5x HDDs) it delivers 110TB as 2x volumes of 70TB must be created – so 2x 70TB RAW at 55TB RAID 5 each.

30TB is lost to RAID 5.

A further consideration is that larger HDDs take longer to rebuild after a failed HDD, hot-swap replacement. This rebuild time or “Recovery Window” for a 10TB HDD may be 15-20 hours, whereas a 20 TB HDD may take 30 to 50 hours in ideal conditions. Under heavy use, HDD activity and system bottlenecks can extend this Recovery Window for a 20TB HDD to 100 hours or more.

Although RAID 5 arrays are usually rebuilt successfully, the recovery process places additional stress on the remaining HDDs. Should there be a second HDD failure during the Recovery Window period, there is an increased risk of errors where the entire array storage data may be lost.

RAID 5 GPT (GUID) format

A RAID 5 array can be formatted as a very large single GPT volume. Whilst this approach reduces RAID5 overhead it is deemed risky when array failure conditions are considered.

VMS Co. can supply servers with other RAID configurations. Please contact us for more information.