raid5 Mixing different brands of drive in RAID5 Array

[+Fahim S. MVC]

Hi -

I have a question. In my server that I am building I have an LSI RAID Controller card which I plan to attach 8 drives to running in RAID5 with one acting as a hot spare.

By the very virtue of 4 drives needing to be 2.5" and 4 drives being 3.5", I have decided for WD RE3/4 (whichever I can get cheaper) for the 3.5" and Seagate Constellation.2 for the 2.5", each disc having a capacity of 1TB.

Looking at the discs I have in the server at the moment, for the sake of playing with the configuration I have 3 250GB Seagate discs, but they seem to be different sizes (I have 2, of one model, which are 232.831GB and 1, of another model, which is 232.886GB).

When building the initial array, as long as I have all of the discs in place, I know the controller will make sure it uses the smaller size of the discs available to it and treat every drive being that size - this is fine.

However, I have a concern, which I am struggling to get my head round:

If I later have a failure and am forced to replace one of the discs with a different brand or even different model of the same brand of disc, then will I be in trouble if it is slightly smaller than the actual capacity of each of the original 8 discs I started with? Whilst I will make sure that I will make every effort to replace with the same brand and model, I can't event guarantee that these discs are still going to be available or easy to get hold of when I need to replace and don't particularly want to keep a stock in case of failure.

I think there is a concept of coerced size that has something to do with this, but it's not clear to me as to how this really works.

I'd be grateful to anyone who could shed some light.