James Bensley wrote:
Lets say I have three drives "knocking" around which are all 1TB SATA II drives but each made by a different manufacturer. I am going to guess that these couldn't be used in a RAID 5? Or could they?
RAID is a manufacturer independent concept. Though depending on who you ask it is typically good to have the same drive and model# in the array, mainly so they have very similar if not identical performance characteristics, if you have some drives that are faster than others then performance won't be consistent.
However could a similar result of 2TBs of data with redundancy be achieved with JBOD?
There's a couple of ways of interpreting JBOD, in my experience the most common way is referring to JBOD as a shelf of dumb disks, often times fiber attached, here is an example of such a system -
http://www.infortrend.com/main/2_product/es_f16f-r2j2_s2j2.asp
Another way of interpreting it is presenting a bunch of disks without any sort of RAID protection to the OS, either individually or in a concatenated group(set by the host controller).
Also regarding RAID 5, three drives of data to one for parity is the max ratio I believe? I.e. to expand this by adding another data drive, the original parity drive would no longer cover this and another would be required, is this correct?
Depends on the implementation, I can't speak for linux software RAID but it is not too uncommon to have 5 data, 1 parity(5+1), or 8+1, and some even go as high as 12+1 or even higher(shudder). The higher the ratio generally the lower the performance especially on writes, and disk rebuilds will take far longer with bigger ratios, resulting in a better chance of a double disk failure during the rebuild.
hardware RAID). With a software RAID is this still achievable?
If the hardware supports it yes. Some controllers don't support hot swap well, especially older ones, and if you yank a drive while the system is running it could crash the system/reboot the box/hang the I/O. But it certainly is possible, just be sure to test it out before putting it into production.
If it was me I would go for a 3Ware RAID card, and do it right, only time I might use software RAID these days is if it is RAID 0, which I haven't done since probably 2001. Was considering it for some new web servers because it doesn't matter if a disk dies if we lose the whole box, performance was the most important. But we ended up going with hardware raid 1+0 anyways.
nate