The SAN is provided by a 3rd party and a different group of our company is responsible for it.

But I'll try to raise the 64k formatting you mentioned. Let's see how they react...

The server we currently replace are three years old. Some of those would easily run for a few more years but due to some policies there'll be a replacement every three years without any further discussion. Is it the rule? Yes. Does it makes sense? No.

If I would have a vote I wouldn't replace half of the server at this time. But then the SAN would be over-sized leading to an even lower number of spindles (what would be your preferred spindle-setup for 8 spindles instead of 15 😉 ). Unfortunately, the folks responsible for the SAN are only calculating by storage space required.