RAID – a small learning

RAID with any filesystem / Storage array or with JBOD it comes with three main benefits.

  • Performance
  • Capacity
  • Integrity

Performance is how fast you can access the data / write the data into the filesystem and it is measured with Input / Output per second aka IOps and usually measured in megabyte per second and millisecond of latency

Capacity is how much it can hold your data, usually GBs to PBs

Integrity is how many disks can fail before you lose all the data,

The main problem of the RAID is you cannot get all the three benefits, to get one you have to sacrifice the other, for example, RAID-0 is both fast and also the high capacity ( full capacity of the disk ) but absolutely no integrity, whereas RAID-1 has the fantastic integrity, fast read ( two sources of data ) but slow write ( data has to write in both the disk before acknowledging the write ) and has half capacity.

RAID 0 aka DISK Stripping has no redundancy but provides the best performance and additional storage. Any drive failure destroys the entire array so raid 0 is not safe at all.

RAID-1 or DISK Mirroring simply mirrors the same data over another drive in the array. This is excellent redundancy as you can lose every drive except one and still have access to the data.
A positive is the RAID read speed is increased by every drive added to the array. The big negative is low capacity and slow write speed speeds. No matter how many drives are in the raid you have the total capacity of a single drive to use. Speed is reduced because every drive gets a complete copy of the same files.

RAID -2, 3, 4 are no longer used by the IT industry.

RAID-5 aka RAIDZ distributes parity along with the data and can lose one physical drive before a raid failure. Because parity needs to be calculated raid 5 is slower than raid0, but raid 5 is much safer. RAID 5 requires at least three hard disks in which one(1) full disk of space is used for parity.

RAID-6 aka RAIDZ2 distributes parity along with the data and can lose two physical drives instead of just one like raid 5. Because more parity needs to be calculated raid 6 is slower then raid5, but raid6 is safer. raidz2 requires at least four disks and will use two(2) disks of space for parity.

RAID-10 aka RAID 1 + 0 is mirroring and striping of data. The simplest raid10 array has four disks and consists of two pairs of mirrors.
Disk 1 and 2 are mirrors and separately disk 3 and 4 are another mirror. Data is then stripped (think raid0) across both mirrors. You can lose one drive in each mirror and the data is still safe. You can not lose both drives which make up one mirror, for example, drives 1 and 2 can not be lost at the same time. Raid 10 ‘s advantage is reading data is fast. The disadvantages are the writes are slow (multiple mirrors) and capacity is low.

Comment below if you any questions related to RAID or if you have any suggestions on this post.

Also published on Medium.

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