K does not charge for the file system, it is "free," and is included
1. when a new set of drives completely replaces ALL the drives in a Server (i.e. the old drive upgrade promo), and
2. when a dealer (or customer) requests the file system be added to a new drive order.
I know you already know this, but for some who might not know, you cannot "mix" drives from different Servers, nor add new drives that also have a new file system installed to an existing Server that is not empty. When requesting a file system be added to a set of drives you are ordering from K, you will receive the following caution:
Cautions (1)
The KFILESYSTEM part numbers should only be used when purchasing an entirely new set of disks cartridges for an empty server chassis. Do not include a KFILESYSTEM part when you simply want purchase add-on disk cartridges to increase the amount of storage in an existing server or Cinema One.
Regarding your drive situation, I'd reach out to K support to have someone look at your system to determine exactly what is happening to those 4 drives, and more particularly your system and "content" before ordering drives. I doubt you plan to replace all 14 drives, so in your case, unless your file system is somehow corrupted, I don't think you would be ordering a new file system. Assuming you indeed have 4 failed drives, replacing those drives, and reinstalling your content (if required) would seem to be the way to correct the problem.
Jim