CompTIA® Server+ : Storage :
Raid Technologies, Features And Benefits
3.1 Describe RAID technologies
and its features and benefits
Important Disk RAID levels:
a. RAID 0: Disk Striping without parity. Minimum
2 disks are required. RAID 0 doesn't provide any fault
tolerance, but read/ write to the disk will improve
b. RAID 1: Disk Mirroring and Disk Duplexing. Disk
Mirroring requires at least two partitions of same size.
Each partition should be on a different physical drive.
In other words, minimum 2 disks are required. For disk
duplexing minimum 2 disks and 2 controllers are required.
RAID 1 provides good fault tolerance, though disk access
is slower compared to disk striping
c. RAID 2: Disk Striping with Error correction.
d. RAID 3: Disk striping with error correction code
stored as parity
This takes a striped array as in RAID 0, then adds
a parity hard disk drive to the array. This parity information
is vital if one drive fails. If a drive should fail
in this situation, the parity drive can be used to restore
blocks that have been broken due to data corruption.
e. RAID 4: Disk striping with large blocks allocation.
f. RAID 5: Disk Striping with Parity. Disk Striping
with Parity requires at least three partitions of same
size, and each partition should be on a different physical
drive. In other words, minimum 3 disks are required
for disk striping with parity. Fault tolerant, less
expensive than disk mirroring. If more than one disk
fails, data can't be recovered. You still need to depend
on tape back up for multiple disk failures.
RAID 5 is similar to RAID 3, except the parity information
is spread across all drives, this allows all drives
to be able to rebuild the array if a drive fails. In
RAID 3 parity is written to only one drive.
Note: compared to disk striping
or disk striping with parity; Disk mirroring has more
overhead, as the entire disk get copied to another disk.
RAID 10 describes Mirrored Striping. It is a mode
0 array, plus a mode 1 array, striped. For example,
if you have striped data into two drives, each drive
is mirrored in RAID 10. That is a total of 4 drives.
RAID is utilized across several platforms: SCSI,
FIBRE-SCSI and IDE are the most common implementations
of RAID technologies.