The more commonly used RAID levels are RAID 0, RAID 1, RAID 0+1, and RAID 5. Each “level” is simply a different
configuration of the RAID standard, each providing certain benefits and performance parameters.
RAID 0
RAID 0 could be said to not be technically RAID. Why? Because it lacks the “R” – redundancy. RAID 0 is basically a
RAID setup that employs the striping I talked about above. This setup requires at least two hard drives to be
configured into a “striped set”. RAID 0 is becoming increasingly popular amongst power users. As discussed before,
this setup offers much higher read/write speeds than normal and will really help to speed up a computer. People who
are into raw speed for gaming, multimedia, etc, will enjoy RAID 0. But, because it lacks the redundancy factor, it
is not typically used in corporate, mission-critical environments. If one drive of the RAID 0 array dies, the whole
array is screwed.
RAID 1
RAID 1 employs the mirroring capability discussed previously. It can, in some cases, provide a little performance
benefit, but it is primarily used for redundancy, pure and simple. With RAID 1, you have the option of attaching a
third drive to the controller. It acts as a spare drive. It is not part of the RAID array, but simply kicks in in
the event that one of the drives fails. The controller would perform an automatic restore to the spare drive,
notify you of the failure, and continue operating as though nothing happened. RAID 1 is used more on corporate
networks andweb servers. Desktop users don’t typically need it, although some who REALLY need that redundancy do
use it on desktop machines.
RAID 0+1
RAID 0+1, as you might be able to tell from the name, gives you the best of both worlds. It can be costly, though,
as it requires at least 4 hard drives to do it. Two of the drives are striped, as in a RAID 0 array, and the other
two are mirrors of the first two. This is the only option for IDE users who want both the speed and the redundancy.
Due to the cost of buying 4 hard drives plus a RAID controller, this is not the most popular option in town. It
does, though, kick ass, and you will find desktop users and web server guys using this.
RAID 5
RAID 5 uses the high performance capability of striping with the increased integrity of the parity bit. The setup
requires at least 3 drives. To see why it needs 3, see the discussion of parity above. By comparing the data on
two of the drives, it can “fill in the blanks” on the third drive, just like solving an algabraic equation. This is
what gives RAID 5 the security. Because both the data and parity info is spread out across all drives, it is often
called “distributed parity”.
RAID 5 is typically not an option for desktop users. It offers the best of all worlds, but typically only SCSI RAID
controllers have the ability to handle it. This means IDE cannot be used, which in turn means this option will
cost a crapload. RAID 5 is typically thought to be used in enterprise servers and the like.
JBOD
I love the name of this one – JBOD, “Just a Bunch of Drives”. No kidding. This is barely RAID at all. It basically
uses the controller to span two drives together into a single drive volume. When one of the disks fill up, it
starts using the other one, transparently to the user. This setup will utilize all the space of the drives, which
means you won’t lose any space with differently sized drives placed on the array. On the flip side, though, it
doesn’t offer any redundancy or performance benefits. You will find that many controllers offer this as an option,
although there’s not a huge point in using it, in my opinion.
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