Intr oduc t ion t o RA ID 31• The number of SCSI channels and SCSI hard drivesComponents and FeaturesRAID versions, or levels, are specifications that describe a system forensuring the availability and stability of data stored on large disksubsystems. A RAID system can be implemented in a number of differentlevels). PERC 3 supports RAID levels 0, 1, 5, 10 (1+0), and 50 (5+0).Physical ArrayA RAID array is a collection of physical disk drives governed by the RAIDmanagement software. A RAID array appears to the host computer as one ormore logical drives.Logical DriveA logical drive is a partition in a physical array of disks that is made up ofcontiguous data segments on the physical disks. A logical drive can consistof an entire physical array, more than one entire physical array, a part of anarray, parts of more than one array, or a combination of any two of theseconditions.Fault ToleranceFault tolerance is the capability of the subsystem to undergo a single failurewithout compromising data integrity, and processing capability. The RAIDcontroller provides this support through redundant arrays in RAID levels 1,5, 10 and 50. The system can still work properly even with a single diskfailure in an array, through performance can be degraded to some extent.Fault tolerance is often associated with system availability (high mean timebetween failure, MTFB) because it allows the system to be available duringthe failures. However, this means it is also important for the system to beavailable during the repair of the problem. To make this possible, PERC 3supports hot spare disks, and the auto-rebuild feature.
