Dell PERC 4/SI - Manual (Page 17)

l The number of physical drives in the disk array
l The capacity of the physical drives in the array
l The need for data redundancy
l The disk performance requirements
RAID 0
RAID 0 provides disk striping across all drives in the RAID array. RAID 0 does not provide any data redundancy, but does offer the best performance of any
RAID level. RAID 0 breaks up data into smaller blocks and then writes a block to each drive in the array. The size of each block is determined by the stripe size
parameter, set during the creation of the RAID set. RAID 0 offers high bandwidth.
By breaking up a large file into smaller blocks, the RAID controller can use several drives to read or write the file faster. RAID 0 involves no parity calculations
to complicate the write operation. This makes RAID 0 ideal for applications that require high bandwidth but do not require fault tolerance. RAID 0 is also used
to denote an "independent" or single drive.
Table 2 -5 provides an overview of RAID 0.
Table 2-5. RAID 0 Overview
RAID 1
In RAID 1, the RAID controller duplicates all data from one drive to a second drive. RAID 1 provides complete data redundancy, but at the cost of doubling the
required data storage capacity.
Table 2 -6 provides an overview of RAID 1.
Table 2-6. RAID 1 Overview
RAID 5
RAID 5 includes disk striping at the block level and parity. In RAID 5, the parity information is written to several drives. RAID 5 is best suited for networks that
perform a lot of small input/output (I/O) transactions simultaneously.
RAID 5 addresses the bottleneck issue for random I/O operations. Because each drive contains both data and parity, numerous writes can take place
concurrently. In addition, robust caching algorithms and hardware based exclusive-or assist make RAID 5 performance exceptional in many different
environments.
Table 2 -7 provides an overview of RAID 5.
Table 2-7. RAID 5 Overview
NOTE: RAID level 0 is not fault tolerant. If a drive in a RAID 0 array fails, the whole logical drive (all physical drives associated with the logical drive) will
fail.
Uses Provides high data throughput, especially for large files. Any environment that does not require fault tolerance.
Strong Points Provides increased data throughput for large files. No capacity loss penalty for parity.
Weak Points Does not provide fault tolerance or high bandwidth. All data lost if any drive fails.
Drives 1 to 32
Uses Use RAID 1 for small databases or any other environment that requires fault tolerance but small capacity.
Strong Points Provides complete data redundancy. RAID 1 is ideal for any application that requires fault tolerance and minimal capacity.
Weak Points Requires twice as many disk drives. Performance is impaired during drive rebuilds.
Drives 2
Uses Provides high data throughput, especially for large files. Use RAID 5 for transaction processing applications because each drive can read and
write independently. If a drive fails, the RAID controller uses the parity drive to recreate all missing information. Use also for office automation and