Can someone explain Raid?

[Sir. Smudge]

I've heard Linus talk about it, but can someone explain it in detail. Some pros and cons would be great.

[Vitalius]

I've heard Linus talk about it, but can someone explain it in detail. Some pros and cons would be great.

Where the data is split between 2 drives. This increases your speed (roughly) by double. Pro: Speed increase

However, if either drive dies, the data is unrecoverable. Meaning you lose everything on the RAID 0'd drives. You do keep all the available storage, however. Con: Increases chance of data loss.

Minimum drive requirement: 2

Where data is copied exactly between 2 drives. You lose half the storage since it's just a copy of what's on the other drive. Con: Lose available storage space.

It doesn't give a speed increase unless you are running Linux or FreeNAS, where it doubles Read speeds (not Writes). Pro (if using certain systems): Doubles Read speeds (like RAID 0).

If one drive fails, the other works perfectly fine, since it's just a copy. A 1:1 backup. Pro: Complete backup of a drive.

Minimum drive requirement: 2

Parity RAID. RAID using calculations to keep your data backed up among multiple drives without losing too much storage space. You lose some storage space, but not 50% like in RAID 0. Con: Loss of available storage space. Pro: Less space lost than in RAID 1 while still getting redundancy (i.e. a drive failure doesn't mean you lose access to your data). 

It's very CPU intensive, and usually means you get around 80% of 1 drive's read/write speeds, meaning you lose a bit of performance, as compared to using a single drive by itself. Con: Lose performance, and taxes CPU.

You can lose 1 drive in RAID 5, 2 drives in RAID 6, and 3 drives in RAID 7 without losing data. However, you then need to replace the drive that died so the RAID can rebuild itself (time consuming and system resource demanding) or risk losing your data should another drive die in succession. Each RAID level gets more efficient, costing less available storage space to use. Pro: Redundancy in increasing numbers of efficiency. 

Minimum drive requirement: 3 for RAID 5, 4 for RAID 6, and 5 for RAID 7. 

There are other RAIDs, but those are the primary ones. ZFS has RAID Z1, Z2, and Z3, but they are pretty much the same as 5, 6, and 7 respectively. 

You can nest RAIDs too, so having RAID 10, or RAID 50, or so on, where you take two RAID 1 or 5 arrays and split them. But that gets increasingly complicated to manage. 

Note: Never use consumer grade drives for Parity RAID. It's a bad idea. Trust me.

[EpicGeekonFire]

You use it to kill cockaroaches and other bugs. 

Pros: Sprayable, direct kill

Cons: deadly ._.

 

I am bored V_V

[jscho]

RAID or (Redundant Array of Independent Disks) is a way of basically combining a whole heap of hard drives into one large pool, or volume.

There are differenct types of RAID such as 0, 1, 5, 6 and 10 being the main ones. Linus has done Tech Quickies on all of them.

 

Linus refers to RAID as "Redundant Array of Inexpensive Disks", but both makes sense and work.

[Sir. Smudge]

What's the best to use even though they have different jobs?

[brob]

What's the best to use even though they have different jobs?

 

None. RAID is not backup. RAIDs other than 0 are designed to provide fault tolerance. It should be used in environments that cannot afford downtime.

 

In my opinion the only time RAID 0 should be used is when one must have a larger drive and the only viable option is more than one smaller drive. Or when speed is of the utmost importance, i.e. more important than reliability.

 

Home systems should do regular, (read daily) backups. If a drive fails it can be easily replaced and restored from backup. If downtime must be minimized a spare drive can be kept so one doesn't need to run to the nearest hdd store.