[G4] EIDE and Ultra ATA RAID

[Ralph Garrett]

Some thoughts on RAID Arrays.

RAID 0, Striping a matched set of drives does not decrease the MTBF for 
the array, the MTBF remains the same as for a single drive. Loss of a 
drive in a striped Array does mean you lose all of the data on both 
drives, but a striped Array can and should be backed up just like any 
other drive.

RAID 1, Mirrored Arrays are used to increase data security by writing 
the same data to multiple hard drives, but there is a performance hit 
on mirrored arrays.

There are several other schemes to improve data security and 
performance but for the desktop user, probably the best solution is to 
mirror and stripe, RAID 10, but obviously that's a more expensive 
solution.

RAID Arrays setup using Disk Utility are called soft RAIDS. The CPU/OS 
has to manage the RAID so you don't get the performance boost you would 
with a hardware RAID controller.

The average desktop user won't see much speed improvement by installing 
a RAID Array but for those who render 3D scenes, edit video/audio files 
or very large Photoshop files there can be a big improvement in 
performance. The most cost efficient way to do this is to use a pair of 
smaller drives (30 to 80 GB's) in a striped array, and use that array 
as a scratch disk only. If a drive fails in the array, very little 
critical data is lost and is usually easy to recreate. You also need to 
be ruthless about clearing files that are no longer needed. I have 
clients erase the scratch Array after they finish every project so they 
start with a clean slate.

You can also gain a small performance boost by using drives in a 
conventional manner attached to multi channel drive controllers, 
storing the OS on one drive and apps on another drive.

HTH

Ralph