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C: RAID Basics
RAID 0
RAID 0 (also known as a stripe set) splits data evenly across two or more disks with no parity
information for redundancy. RAID 0 is not redundant. RAID 0 is used to increase performance,
and can be used as a way to create a small number of large virtual disks out of a large number of
small physical ones.
RAID 0 can be created with disks of differing sizes, but the storage that is added to the array by
each disk is limited to the size of the smallest disk.
Example
: A 120GB drive is striped with a 100GB drive. The size of the array will be
200GB (100+100).
RAID 0 is useful for read-only NFS servers where mounting many disks is time-consuming and
redundancy is irrelevant.
JBOD (Just a Bunch of Disks)
JBOD is a popular method for combining multiple physical disk drives into a single virtual one.
Disks are merely concatenated, beginning to end. JBOD is commonly used to turn several
odd-sized drives into one useful drive.
One advantage JBOD has over RAID 0 is in the case of drive failure. When a single drive of a
RAID 0 array fails, usually it will result in the loss of all data in the array. When a drive failure
occurs in a JBOD array, only the data on the affected drive is lost.
RAID 1
RAID 1 creates an exact copy (or mirror) of all the data on two or more disks. This is useful where
redundancy is more important than using all of the disk storage capacity. The array in a RAID 1
can only be as big as the smallest member disk. An ideal RAID 1 set contains two disks. Since
each member can be addressed independently if the other fails, reliability is a linear multiple of
the number of disks in the array. RAID 1 benefits most when an independent disk controller is used
for each disk.
Seek time with a RAID 1 remains low because each drive can be accessed independently, and the
requested sectors can be split evenly between disks. When writing, the RAID 1 array acts like a
single disk because all writes must be written to all disks.
Summary of Contents for InfiniteStorage 3000
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