Using 4 hard drives in RAID-0 configuration?

This article is a bit technical and relies on know-how from a previous article I've written about RAID.

In brief, the word 'RAID' is a techy-term which stands for Redundant Array of Independent (or Inexpensive) Disks. A hard disk array is simply a bunch of hard drives chained together.

Benefits of using RAID are generally two-fold, and include: increased file read / write performance (known as RAID-0), and data redundancy for backup purposes (known as RAID-1). I've previously written an article about RAID if you would like to read up on it. It is very simplistic and explains RAID essentials in a bit more detail.

Recently, Pat P. sent me this email:

" A while back you helped me install a RAID-0 configuration on my PC. I'm wondering if it can be done differently? I set both hard drives as a master ... could I set one as a slave so I can [add two more drives to the array Thanks for your help. "

My response:

Most IDE RAID controllers which support RAID-0 have only 2 I/O (input / output) channels for communication. Each channel is capable of 2 hard drives, yielding a maximum of 4 [IDE] hard drives chained to the RAID controller.

Side note: IDE is an interface which can handle up to 2 devices on the same channel, typically set as a Master or Slave. 99.99% of all home computers have an IDE [hard drive] interface built onto the main board. RAID controllers come in two primary interfaces: IDE and SCSI. SCSI and SCSI RAID controllers are for more higher-end systems (such as servers) and can chain more than 2 devices.

More about the SCSI interface:

http://savage.net.au/Ron/html/scsi-tutorial.html

More about RAID interfaces [SCSI and IDE]:

http://www.pcguide.com/ref/hdd/perf/raid/conf/ctrlInterfaces-c.html

Here's what a typical IDE RAID-0 configuration looks like:

• I/O Channel 0: Hard Drive #1 (Master)
• I/O Channel 1: Hard Drive #2 (Master)

Recall that RAID-0 is performance based. Both drives are on separate channels of communication, transfer double throughput, and yet act as 1 physical unit.

Getting back to Pat P.'s question: adding 2 more hard drives to a 2-channel IDE RAID controller -- without destroying the current array -- would essentially result in a RAID-0+1 array, and would look like this:

• I/O Channel 0: Hard Drive #1 (Master), Hard Drive #3 (Slave)
• I/O Channel 1: Hard Drive #2 (Master), Hard Drive #4 (Slave)

For simplicity, assume all 4 drives are 80 gigabytes in size.

If this was a RAID-0+1 configuration, there would only be 160 gigabytes of usable (tangible) storage, since:

• RAID-0 combines both Master drives (2 x 80 gig = 160 gig) and,
• RAID-1 simply mirrors the RAID-0 array but is not tangible.

And yet, another possibility?

I've never tried this, but: I believe it is also possible to use the identical layout (as illustrated, above) and redefine the array to be 2 x RAID-1. In this case, there would be no RAID-0 "striping" (ie: speed performance); the total tangible storage in this configuration would be 2 drive letters containing 80 gigabytes each (the other 2 are used for mirroring / backup).

Pat wrote back again:

" Thanks, Dennis! I guess I can't accomplish what I had in mind. I wanted to take 2 x 80GB hard drives + 2 x 40GB drives and have 2 separate RAID-0 arrays ... I don't want to mirror the existing RAID-0 array [especially since the other hard drives aren't 80 gigabytes in size]. PS: I have the RAID built in the motherboard. "

My response:

This is still possible; however, an additional RAID controller is required. As far as choosing which RAID to boot from: you should be able to define your first / second / third (etc) boot device in your computer's CMOS setup.