so lets say i have 2x 60gb SSD's, 120gb in a raid0. do i format each one as much as i can and then leave 20% of the available, usable, disk space free on each (so 40% over the 2 drives) or do i leave 20% of each drive unformated??
Sorry for the temporarily deleting of the post... i've just realised that i've cocked up on the maths for the SFs... i'll also post this as a new thread as i need to make it clear that i've made a major mistake. Now, the reason for the issue is that, whilst every other consumer drive uses ~7% OP (which is what i'd based the 21.5% on when i first did the calculations looking at another SSD controller), the SFs actually either use ~28% or ~13%. These though are approximate figures (& it varys slightly between capacities) so the best fit compromise that's close enough to all of the models is to work to 27% & 14%. Right so the basic maths for OPing a SF is actually - 14% of 100 leaves 86%... & 27 of 100 leaves 73%... So 100/86 x 73 = ~85 -> you have to reduce by ~15%. Now, this of course isn't exact, but it's a rule of thumb way to get a quick figure... [NB the above is for the SFs without extended OP only - the 21.5% still applies to SSDs with other controllers which have a ~7% f/w OP] Now, re your actual question (but using the 15%), imagining that you had 2x 100GB (formatted capacity) drives which were each reduced by 15% 85% of 100GB is (obviously) 85GB -> 85GB x2 = 170GB & 85% of 200GB is also 170GB So, taking 15% off of the array size is the same as taking 15% of each & is only a 15% reduction in the total capacity.
