All anecdotal. I'm glad they work for you, but inconsistency is the key and the primary reason why you wouldn't want to use them in a server. They are not designed for servers, for RAID, or for high-performance enterprise data applications. 2TB is the hard limit on the PERC 6 for physical disks, but every unsupported drive you put in there will be a completely different experiment, and you are bound to see different results with different makes, models, sizes, cache, speed, geometry, programming/firmware, etc. 
We recently purchased an R900. I tried to use 2 western digital black 1TB hard drives set up in a RAID1 The array was successfully created and was seen as Optimal. But after a short period of time I get a an HDD fault on that array (both drives blinking amber). I bought  a new WD Black 1TB drive thinking that I might have a bad drive. I attempted to create a new array with the new drive and got the same error but again the RAID controller saw no problem with the array(but still two blinking amber lights). I was beginning to think that my PERC 6i card might be bad. As a test I wiped one of my new WD 1TB Black drives inserted jut that drive in the box and booted up. It was green for the first minute or so after boot and then it began blinking amber with a HDD error again. I tried the other 3 of my WD 1TB drives one by one with the same result. Lastly I found an older 120GB WD drive and tried that drive. This time there was no HDD Error message and the light has remained green. I doubt that I have 4 bad WD 1TB Black Drives. My guess is that the r900 has a drive capacity limit and that a 1TB Drive is too large. Can anyone confirm this and tell my what the drive size limit is for the R900 using 2.5 drives?     
R900 2.5 drive size limits?