There are limited was which a NAS can be used in an Aperture workflow.

For a detailed post on the topic, visit “Network Drives (NAS) and Aperture”, a post from August 2010

Apple’s own article on the topic is here: support.apple.com/kb/TS3252

Here are some key take-aways though:

“Always use a locally mounted Mac OS X Extended formatted volume to store your Aperture library. Mac OS X Extended is the only file system supported by Aperture.”

In other words, your Library should always be on a local drive, and one formatted as a Mac OS X disk. Many USB thumb drives are FAT32 or other hyrbid formats and can’t be reformatted as Mac OS X Extended, so should not be used.

“If you store your Aperture library on a volume that is formatted FAT32 (a file system commonly used on Windows PCs), you may encounter issues including poor performance, data corruption, and data loss. Referenced images stored on FAT32 volumes may sporadically go offline. Many external drives come pre-formatted as FAT32. Use Disk Utility to format new external hard drives as Mac OS X Extended before using them with Aperture.”

In other words, don’t use any FAT32 volumes for any part of Aperture, period.

“Also, it is strongly recommended that the Aperture library be stored on a locally mounted hard drive. Storing the Aperture library on a network share can also lead to poor performance, data corruption, or data loss.”

In other words, it’s technically OK to have your referenced masters on a NAS (assuming it’s a Mac OS X Extended volume), but under no circumstances should your Aperture library be on a network volume of any kind.

But doesn’t that mean I can’t share my library among everyone in my house/office/etc.?

That’s right. Aperture is not a multi-user photo database application. If you really want to share, the most effective way is the simplest way—sneakernet. That means you put your Library on a fast external FireWire or Thunderbolt drive, and walk said drive from computer to computer. Only one person can use it at a time, but that’s just the way it is. Don’t tempt fate. These are your photos we’re talking about here.