Raid 0, Raid 1 – HP ProLiant ML110 G4 Server User Manual
Page 15
Understanding RAID 15
When selecting a RAID level for your system, consider the following factors.
Table 4
Comparison of RAID level features
RAID 0
RAID 1
RAID 10
Data redundancy
No
Yes
Yes
Amount of physical drive capacity used for data storage
100%
50%
50%
Read performance
Superior
Very high
Very high
Write performance
Superior
Very high
Very high
Built-in spare drive
No
No
No
Minimum number of drives
2
2
4
Maximum number of drives
4
2
4
Physical drive utilization, read performance, and write performance depend on the number of drives in the array.
Generally, the more drives in the array, the better the performance.
RAID 0
A RAID 0 array uses from two to four disk drives and provides data striping, where data is distributed evenly
across the disk drives in equal-sized sections.
RAID 0 arrays do not maintain redundant data, so they offer no data protection. However, compared to an
equal-sized group of independent disks, a RAID 0 array provides improved I/O performance.
The size of a drive segment is the size of the smallest disk drive in the array. For instance, an array that consists
of two 250-GB disk drives and two 400-GB disk drives has a drive segment size of 250 GB. This array thus has
1,000 GB (= 4 x 250 GB) of usable drive space, all of which can be used to store data when the array is used
to build a RAID 0 logical drive. The array also has 300 GB of drive space that is unusable in the context of this
particular collection of drives.
The following figure illustrates this example, with HD1-HD4 representing the disk drives, LD representing the
logical drive, D1-D9 representing data fragments, and (ND) representing sections of the drive that are unused.
RAID 1
A RAID 1 array is built from two disk drives, where one disk drive is a mirror of the other (the same data is stored
on each disk drive). Compared to independent disk drives, RAID 1 arrays provide improved performance, with
twice the read rate and an equal write rate of single disks. However, capacity is only 50% of independent disk
drives. If a RAID 1 array is built from different-sized disk drives, the size of the drive segment is the size of the
smaller disk drive, as with RAID 0.