Onboard vs Dedicated aside (understandably, Raid 5 requires more processing power for parity), I had a question/statement in regards to all the Raid recommendations I have seen here. Why is Raid either not recommended off the bat, or the recommendations that do come out for Raid 1 or Raid 10?

The way I see it is as follows. For a theoretical array of 4 500GB drives, the following statements should be true as I understand them.

Capacity
Raid 0 = 2TB (capacity = total of all drives, minimum 2)
Raid 1 = 2x 500GB (2:1 ratio, minimum 2 per set)
Raid 10 = 1TB (2:1 ratio, minimum 4)
Raid 5 = 1.5TB (capacity = total of all drives minus 1, minimum 3)

Redundancy (NOT BACK UP)
Raid 0 = NONE
Raid 1 = Single Drive Failure per mirrored set
Raid 10 = Single Drive Failure per mirrored set
Raid 5 = Single Drive Failure

Performance
Raid 0 = Fastest, performance increases with drive count
Raid 1 = Possible boost in speed for READ, no gain to possible loss (if noticeable) elsewhere
Raid 10 = Similar performance to its equivalent drive Raid 0 (ie 3 Drive Raid0=6 drive Raid 10)
Raid 5 = Between Raid 0 and single drive performance, goes up with drive count. processor intensive

With these statements, it seems to me that on a price vs capacity+performance comparison, Raid 5 comes out as the winner, the only fault being the extra processing power required (on software raid at least) for parity information on writes. otherwise, for the price of a single extra drive, one can have a similar level of fault tolerance, 66% of the available capacity (this also increases as drive count goes up, 75% available in a 4 drive array etc.) and descent read/write performance as compared to a 2 drive Raid 1 array with only 50% available capacity. This also allows gamers to have their boost in performance and have redundancy to boot. With more and more software based controllers offering this as an option, why not?

Disclaimer for those reading this to gain an idea of what array to go with, Raid for redundancy does NOT cover loss of data due to formatting, accidental deletion, viruses or any myriad of events leading to data loss. these do however offer protection against data faults and hardware failure (except Raid 0 with ZERO protection). having a Raid array is NO EXCUSE to not back up important data!

Why is Raid either not recommended off the bat, or the recommendations that do come out for Raid 1 or Raid 10?

The way I see it is as follows. For a theoretical array of 4 500GB drives, the following statements should be true as I understand them.

Most people aren't planning on having 4 identical hard drives. Or even 3, the minimum required for RAID 5.

Also, it seems that most people seem to want RAID for either performance or for redundancy, not both. It's all a matter of priorities. If I were to buy multiple drives for an expensive system, I'd probably RAID 5 them (for simplicity, if nothing else). But I'm cheap.

I just wanted to clear up the slightly vague statement quoted (in bold), and also highlight the difference between RAID 0+1 and RAID 10 (RAID 0+1 not having been mentioned). They may perform identical and have the same capacity, but they are very different, and offer different redundancy.

RAID 0+1 (by far the more common)
Config - a mirror of two striped (RAID 0) sets.
Redundancy - UP TO TWO drives may fail without data loss, as long as the two drives that fail are part of the same stripe set (e.g. Drives 1 and 2 in pic-A below). If one stripe fails (one or both drives), it is still mirrored by the other striped set so no data is lost. If one drive from each stripe fails, then all data is lost.

RAID 10 (rarely suppported by onboard RAID controllers)
Config - a stripe set of two mirrored (RAID 1) sets.
Redundancy - UP TO TWO drives may fail without data loss, as long as the two drives that fail are part of different mirror sets (e.g. Drives 2 and 4 in pic-B below). So one drive of each mirror can fail without data loss, but if both drives of a mirror fail then all data is lost.

I don't remember where I read this, or the rational behind it (something based on statistics) but RAID 10 is considered to be superior to RAID 0+1.

Attempt at demonstrating the difference graphically:

PIC-A RAID 0+1 PIC-B RAID 10
______MIRROR______ ______STRIPE______
| | | |
_STRIPE_ _STRIPE_ _MIRROR_ _MIRROR_
| | | | | | | |
Drive1 Drive2 Drive3 Drive4 Drive1 Drive2 Drive3 Drive4

Hope this makes sense and helps add to the understanding of RAID!

Yet both are useless on the desktop. That's why by the time you start thinking RAID 5 you should be thinking RAID 5 or RAID 6.

In other words, I guess I am saying that if you're thinking RAID 5 you're really not a typical consumer, and then the increased cost is justified to improve redundancy. 'Cause the cost of downtime in most enterprise use is too high.