I can totally understand that a shared network storage is the first option to think of, but maybe an offsite object storage is a better solution?
Think of an 12-factor App with ephemeral storage where you separate code from content + abstract the file system.
How to implement: take your WordPress (Drupal …) and plug in an AWS S3 add-on. This transfers all files to a cloud storage ans serves them from there.
Disclaimer: I am fortrabbit co-founder. We are specialized in scalable PHP hosting and we used to have an attached network storage for our Old Apps are now replacing with an Object Storage instead.
Frank Lämmer
been there, done that