StorCase Technology FC-to-SCSI Single & Dual RAID - Manual (Page 157)

144 Appendix B - Array Basics
StorCase Technology, Inc. FC-SCSI Dual RAID Module User's Guide - Rev. A01
RAID 50
RAID 50 arrays contain redundant information in the form of parity data, which is calculated
block-by-block for all user data. The partity information is distributed across the disks in the
array and occupies the equivalent capacity of approximately one disk. Data is interspersed
with the parity information. If one disk in the array fails, the data on the failed disk can be
reconstructed from the parity data and user data on the remaining disks. Two disks must fail
before the entire array fails.
The read performance of a RAID 5 array is excellent - comparable to that of a RAID 0 array.
Write performance is lower than that of a RAID 0 array, because write operations involve
calculating and writing new parity data, as well as writing the new user data.
Volume Sets
A volume set is a host-accessible LUN that maps to a single disk in the array, similar to JBOD.
Volume sets are non-redundant and have a capacity slightly less than the physical disk they
are created from. Volume sets are useful if a single disk is available and not used as a spare.
Mixing Disks from Different Manufacturers or with Different Capacities
An array can contain different models of SCSI disks, even disks with different capacities (an
array can include a 4GB disk and a 9GB disk). However, if disks with different capacities are
mixed, the logical capacity of all other disks in the array is determined by the smallest disk
(regardless of RAID level). To maximize disk capacity, use disks of similar size.
Mixing Disks on Different RAID Controller Channels
The FC-to-SCSI RAID Controller Module has four drive channels. An array can consist of disks
on different channels of the same RAID controller.