Common Name(s): RAID 0. (Note that the term "RAID 0" is
sometimes used to mean not only the conventional striping technique described here but
also other "non-redundant" ways of setting up disk arrays. Sometimes it is
(probably incorrectly) used just to describe a collection of disks that doesn't use
redundancy.)
Technique(s) Used: Striping (without parity)
Description: The simplest RAID level, RAID 0 should really be called
"AID", since it involves no redundancy. Files are broken into stripes of a size
dictated by the user-defined stripe size of the array, and stripes are sent to each disk
in the array. Giving up redundancy allows this RAID level the best overall performance
characteristics of the single RAID levels, especially for its cost. For this reason, it is
becoming increasingly popular by performance-seekers, especially in the lower end of the
marketplace.
|
This illustration shows how files of different sizes
are distributed between the
drives on a four-disk, 16 kiB stripe size RAID 0 array. The red file is 4 kiB in
size; the blue is 20 kiB; the green is 100 kiB; and the magenta is 500 kiB.
They are shown drawn to scale to illustrate how much space they take
up in relative terms in the array--one vertical pixel represents 1 kiB.
(To see the impact that increasing or decreasing stripe size has on the
way the data is stored in the array, see the 4 kiB and 64 kiB stripe size
versions of this illustration on the page discussing
stripe size issues.) |
Controller Requirements: Supported by all hardware controllers, both
SCSI and IDE/ATA, and also most software RAID solutions.
Hard Disk Requirements: Minimum of two hard disks (some may support
one drive, the point of which escapes me); maximum set by controller. Any type may be
used, but they should be of identical type and size for best performance and to eliminate
"waste".
Array Capacity: (Size of Smallest Drive * Number of Drives).
Storage Efficiency: 100% if identical drives are used.
Fault Tolerance: None. Failure of any drive results in loss of all
data, short of specialized data recovery.
Availability: Lowest of any RAID level. Lack of fault tolerance means
no rapid recovery from failures. Failure of any drive results in array being lost and
immediate downtime until array can be rebuilt and data restored from backup.
Degradation and Rebuilding: Not applicable.
Random Read Performance: Very good; better if using larger stripe
sizes if the controller supports independent reads to different disks in the array.
Random Write Performance: Very good; again, best if using a larger
stripe size and a controller supporting independent writes.
Sequential Read Performance: Very good to excellent.
Sequential Write Performance: Very good.
Cost: Lowest of all RAID levels.
Special Considerations: Using a RAID 0 array without backing up any
changes made to its data at least daily is a loud statement that that data is not
important to you.
Recommended Uses: Non-critical data (or data that changes infrequently
and is backed up regularly) requiring high speed, particularly write speed, and low cost
of implementation. Audio and video streaming and editing; web servers; graphic design;
high-end gaming or hobbyist systems; temporary or "scratch" disks on larger
machines.
Next: RAID Level 1
