A Quick Hit on RAID Levels

These are written by my own fair hand with nothing copied from Wikipedia, so I accept any errors to be my own.

RAID-0

RAID-0, otherwise known as a Stripe without Parity is a method of pooling two or more disks together into a single logical disk. Although consisting of multiple drives, the OS will only see one disk with the total capacity of all of the provisioned drives. Although attributed as a RAID version, RAID-0 provides no protection for the data and there are no parity bits or duplicate copies of the data on any of the disks – If a single disk fails, all of the data which is stored on that disk is lost and the volume will enter a degraded state.

This level gives the highest value for money as every disk you add grants the full amount of storage, but you get no protection for that money, so it should not be used by itself as a data protection solution.

RAID-1

Otherwise known as Mirroring, RAID-1 provides the simplest level of data protection. Two disks are mirrored, so that they are exact copies of each other. In the event of a single drive failure, the other drive takes up the role as the single serviceable disk and performs all of the I/O. Until the failed disk is replaced however, the data is at risk as should the second disk fail then you will have no more copies of the data.

RAID-5

The most commonly used RAID method in older business systems, RAID-5, otherwise known as stripe with parity, requires a minimum of three disks. The storage capacity of the array equals the capacity of two of the disks. The capacity equal to the third disk is used to store the parity data. Two of the three disks can simultaneously fail in RAID-5 and the parity data on the last remaining disk is able to recreate the existing data to it’s full healthy state.

Read performance on RAID-5 is good, however write performance is slow due to the overhead to write the parity data, especially on low grade performance on-board RAID controllers seen on modern day motherboards.

RAID-10

My personal favourite, RAID-10 is what is known as a hybrid RAID or nested RAID technology. It uses a recommended minimum of four disks, although in some configurations can work with two. RAID-10 is actually correctly noted as RAID-1+0. This means RAID-1 combined with RAID-0. A stripe without parity (RAID-0) offers good read and write performance, whilst offering maximum storage capacity, but it offers no protection. RAID-1 Mirror offers good performance for both reads and writes, but the performance is below that of RAID-0. RAID-1 provides the protection of a second copy of all of the data.

RAID-10 fixes this by backing each striped disk with a mirrored copy. In a four disk RAID-10 configuration, the capacity of the volume is half that of the disks total (Eg. 4x 2TB disks gives a physical disk size of 8TB, and a usable disk size of 4TB).

RAID-10 gives you the performance of RAID-0 plus the added performance benefit of having a second disk spindle hitting each I/O, in theory halving the seek time to read or write data to the disk, plus the protection benefit of a second copy of all of the data should one drive fail. In RAID-10, two of the four drives can fail at any one time, however there must be one drive from each Mirror set available to complete the Stripe.

richardjgreen

Richard works as a Cloud Consultant for Fordway Solution where his primary focus is to help customers understand, adopt and develop with Microsoft Azure, Office 365 and System Center. Richard Green is an IT Pro with over 15 years' of experience in all things Microsoft including System Center and Office 365. He has previously worked as a System Center consultant and as an internal solutions architect across many verticals. Outside of work, he loves motorbikes and is part of the orange army, marshaling for NGRRC, British Superbikes and MotoGP. He is also an Assistant Cub Scout Leader.