The catalog is in reality a database. When using databases there are issues with record locking. Your images can be on the network drive. The catalog and associated files must be on a local drive.
Do you really have 8 TB of Lightroom catalogs? I think we have terminology confusion here. The catalog is the database that keeps track of where the images are. But the images are not in the catalog. The catalog is a database that is used to manage the images.
Yes, I really have 8 TB of photography. Its from the past 10 years of dozens of worldwide photography jobs. Granted, not all of it is in Lightroom yet, but much of it is. I used Aperture until Apple abandoned all of its professional software development and have been moving to Lightroom for a while now. Aperture is able to use the NAS as a storage drive, no problem and it uses a database as well, so I really don't see why Lightroom can't do it.
I have an 8 TB Drobo connected by Firewire to my iMac and storing photos on it for Lightroom (and Aperture prior to that) and it works fine. But it's filling up and I wanted some archive storage so I didn't have to have Lightroom catalogs and Aperture libraries on it I really don't use on a regular basis. So I got the Drobo FS800 loaded up with 12 TB of space as a network storage server to make sure everything is safely backed up. I am slowly converting my old Aperture libraries to Lightroom, one at a time as well as using Lightroom for everything I have done for about the last two years.
But it is completely impractical to have to store the pictures and catalog on the NAS Drobo, then have to copy it all over to a local drive if I ever want to find a photograph in on a Lightroom catalog. It will takes hours if not a day to do that, just so I can open it. So I may see if I can store the pictures on the NAS Drobo but keep the catalog on the local Drobo. But I hate the idea of not keeping everything together. It something happens and the shots getting separated from the catalog, I have no idea what will happen or if it will be easy to re-connect the media. I also want to keep a backup of the catalog, but I think the built-in catalog vaults will do that.
But again, Apple's Aperture could keep everything together and has not problem pulling it off a NAS, local drive or anywhere. Really hard to imagine why Adobe can't do the same thing, especially since Aperture is overall so obsolete in every other way to Lightroom by now. Guess I need to try a few things and see if I can make this work. But really not comfortable splitting catalogs up on different drives than the picture files are located.
You still don't have your terminology straight. Your images are not in Lightroom catalogs. Your images are in folders on your network drive. The catalog is a database that manages the images that you want to import into Lightroom. The import process does not put your images "in" the catalog. The import process simply establishes a pointer between Lightroom and where the images are located.The catalog and associated files in the catalog folder cannot be on the network drive. They have to be on a local hard drive or on an external hard drive connected to the computer. But the catalog can point to and provide access to the images that are on your network drive.
I do understand that, but what are the issues with having the catalog on one drive/location and the image files on another drive? For example in Premiere, files can get moved (and it happen ALL the time) when you get a "Media Off Line" issue when a reference the project (which is a database) refers to a file it can no longer find. You need to reconnect the media by having Premiere locate it where ever it moved to or you put the file back. Not fun, but it works. If that happened in Lightroom, what happens? Do I need to re-connect the catalog to where the files are? Aperture took care of that for you and unless you specifically told it to reference a photograph file where it was instead of bring it into it's library (I know that is not what Lightroom does), it was almost impossible to separate the database from the image files. You coped the entire "package" from one drive to another as essential one file (which contained the database AND picture files), so it prevented anything from ever getting disconnected or separated. Again, I understand LIghtrioom does not do that, but the .DNG files in one folder on one drive and a catalog that points to them on another drive really kinda scares me. For example...
My NAS Drobo has a folder with pictures form, say my last China trip. LOTS of shots, maybe over 1000 .DNG shots. My local hard drive has the Lightroom catalog that points to all those .DNG's....my local hard drive crashes and just say I loose it. Or my computer is destroyed and I need to get a new computer (it's happened, regrettably). I pull up a backup of that catalog, I load it up in Lightroom, will that catalog (database) need to somehow be re-connected to that media? How does it know where they are, especially if the NAS Drobo, say, loads with a difference volume name or something. Doing my best to explain what I mean, so I apologize if its over convoluted.
If your network drive has the same name or drive letter designation or what ever as they did when the backup was made, then no. There will not be any relinking necessary. The folder that contains the catalog and other files can be on any local drive, internal or external. Lightroom doesn't care what drive that is on as long as it is a local drive. It's the way you have to do it if you're going to use Lightroom. You can backup your catalog to the network drive. If your computer crashes, or your hard drive in your computer goes bad, you replace the computer or the hard drive and reinstall Lightroom. Then you can copy that catalog file from the backup folder on the network drive back to your local hard drive and you are back in business.
>I do understand that, but what are the issues with having the catalog on one drive/location and the image files on another drive?
None. The implementation of this is not so slick as it was in Aperture but it works just fine. I keep terabytes of images on separate hard drives and they are all referenced in my main Lightroom catalog. To edit them in Develop, all I have to do is hook up the correct hard drive but you can do everything else such as keywording, slideshows, etc. just from the previews in the catalog. It works the same for NAS. Even if you are not near your NAS network, Lightroom will just work fine and show you the images but you won't be able to use Develop. Keep your catalog on your local hard drive and put the images on your NAS. That will work just fine and will make Lightroom feel about as fast as having all images on your local hard drive. You'll just have to relink the files after you move them inside your Lightroom catalog. (see here for how that works: Re-linking Files and Folders in Lightroom « Julieanne Kost's Blog and thousands of other tutorials on this on the web if you google for it). You can also move them inside Lightroom but when you're dealing with this many images I would not attempt that and use the finder to do that.
Just for discussion sake, let's say that your network drives are drives X, Y, & Z. Your catalog is on your system drive, drive C. Your catalog knows where your images are located, let's say on drives X & Y. Now let's say that you attach an external drive, drive D and move your catalog onto that external hard drive. When you start Lightroom and open the catalog in its new position, your images are still on X & Y. So there will be no confusion. You can let Lightroom back up that catalog on to drive Z. If you ever need to restore one of those backups, you restore it back to drive D, and all of the drive letters remain the same and business continues.