Type of Raids

RAID 0 has the best performance and capacity, but the lowest availability (no fault tolerance). If one drive fails, the entire array would fail because part of the data is missing without any ways in recovering them.

RAID 1 has the highest availability but lowest capacity, it requires using twice the number of drives . Performance is roughly the same as when using a single drive, although in some cases the dual write may be somewhat slower.

RAID 0+1 offers some performance improvements by combining striping and mirroring, but capacity is low since the mirror requires a duplicate set of drives.

RAID 3 has high performance and middle capacity, but the availability is lower when compared to RAID 1

RAID 5 has moderate benefits in all three areas. Read performance can be as fast as RAID 0, but write performance is slower, since the parity information must be calculated and written along with the data. Capacity is higher than for RAID 1 but it does not use striping, since the array use additional space for parity information, Availability is high with RAID 5 because of fault tolerance?If a drive fails, the missing data is recalculated from remaining operation drives.

Term of Hot Swap
The term "Hot Swap" refers to the common practice of either inserting, or removing SCSI disk drives in an operating bus, typically used in RAID subsystems or JBOD (just of a bunch of disks) environments. The ability to "Hot Swap" a disk drive is beneficial to customers. It allows them to remove potentially defective drives from the system, or upgrade capacity without having the inconvenience and expense of taking the entire system down to replace the drive. The ANSI documents cover this function under the chapter heading "Removal and Insertion of SCSI devices". Four distinct levels of functionality are defined in Table A.

The term "Hot Swap" is not actually defined in the ANSI standards, or the draft standards under development. It is interpreted as "the very restrictive Level 4 Removal and Insertion of disk drives." To avoid confusion, the two ter ms are linked together as "Level 4 Hot Swap."

The main difference between Level 4 and the easier levels is that the bus is allowed to operate (move data or operate in any legal SCSI bus phase). Since inserting a disk into any powered bus will result in some level of electrical transients, it is necessary to insure that those transients do not interfere with, or corrupt the control of data signals present on the bus.

Defining transfer rate
ATA-100: 100 MegaBit / sec.
ATA-133: 133 MegaBit / sec.
Ultra SCSI & Fast Wide SCSI: 20 MB/ sec.
SCSI III (or Ultra Wide SCSI): 40 MB/ sec.
Wide ULTRA II SCSI (LVD): 80 MB/ sec.
ULTRA III & 160: 160MB/ sec.