SoftRAID 3 Manual Excerpts:
Understanding SoftRAID
SoftRAID 3 is an application and disk driver which allows you to maximize the performance of your hard disks to meet your computing needs. It is a software implementation of RAID. RAID stands for Redundant Array of Independent Disks. It describes a way of arranging data on multiple disk drives so they can be used as one volume. In the past, RAID has only been available as a separate external box which contained an array of disks and the software to run them.
SoftRAID 3 gives you the benefits of RAID for your existing disks without the need for any other supplemental hardware or software.
Disks and Buses
SoftRAID 3 works with five types of hard drives or disks: FireWire, USB, SCSI, ATA and Fibre Channel. These disks connect and communicate with the Mac via buses. Buses are made up of: a) the cables which attach the disk to the Mac, b) the chips which send signals along the cables, and c) the software which controls the chips. FireWire, USB, SCSI and ATA are the types of storage buses supported by SoftRAID 3. Fibre Channel is a speedy implementation of the SCSI bus.
Disks differ in their performance, their portability, and their cost. Most Macs come with ATA disks built in. SCSI is a higher performance and more expensive disk; a FireWire disk is slower but much more portable. Fibre Channel is very fast, very expensive, and not very portable.
Drivers, Volumes and Partitions
The Macintosh communicates with hard disks using drivers. The driver gives instructions to the disks on how to distribute data coming from the Mac onto the disks. Disk management software, such as SoftRAID 3, uses drivers to create volumes on disks. Volumes are discrete entities made up of one or more partitions from one or more disks. Partitions are blocks of sectors on a disk assigned by the driver to a specific volume.
Before a volume can be created on a hard disk, the disk must first be initialized. Initializing a disk involves writing information to the beginning of the disk so a Macintosh can recognize it. Internal disks which come with the Macintosh are initialized with Apple’s Disk Utility application. Disks which are purchased from vendors other than Apple are often uninitialized or have been initialized to work on a PC. Disks must first be initialized with the SoftRAID application before SoftRAID can recognize them.
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Understanding RAID
SOFTRAID 3 can create non-RAID, Stripe (RAID 0) and Mirror (RAID 1) volumes. The advantages of combining disks into RAID volumes are:
Increased speed when reading data off the disks and/or
Increased security from having ongoing data backup.
Non-RAID A non-RAID or standard volume consists of one disk drive. The speed of reading data off of a disk is physically constrained by how fast the reading mechanism, or disk head, can read data from the spinning disk.
Stripe (RAID 0) If the data, instead of being clustered on one disk, is evenly distributed over two or more disks, each disk head can be reading or writing a part of the data simultaneously. A Stripe volume distributes the data across all the disks. The more disks used in a volume, the faster the reading and writing.
Mirror (RAID 1) When all of the data is written to each of the disks, a Mirror volume is created. This makes the backup of data an ongoing process. If one disk fails, the data is intact on the other disks in the volume. SoftRAID 3 enhances RAID 1 by allowing more than two disks in a Mirror volume and by making reads as fast as those from a RAID 0 Stripe volume.
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