The Lightroom Catalog: Storage Considerations

This is the second article in my series about the Adobe Ligthroom catalog. You can find the previous articles here:

The Lightroom Catalog: the Basics

Where Should You Store Your Catalogs?

One of the questions about the Lightroom catalog I get asked most frequently is certainly:

Where do I store my catalog?

In order to answer this question, I will first ask you to consider what I wrote in the previous article:

Note that the catalog does not contain the images themselves, only a pointer to each image’s position on your disk, that is its path.

An immediate consequence of this fact is that it is possible, and also quite advisable in many cases, to store the catalog on a different device than the one where the images are stored.

In order to make a decision on where to store our catalog or catalogs, it is important to know how big can the files that make up a catalog be. To give you an idea, here are the files that make up one of my biggest ones, cataloguing more than a hundred thousand images.

File name	Size
Helper	1.4MB
Previews	70.71GB
Smart Previews	8.41GB
Catalog	1.29GB

Note that all the information about the images is contained in the catalog file itself (.lrcat). The previews can always be rebuilt if they are lost and it’s possible to change the way previews are maintained by opening the Catalog Settings from the Lightroom menu.

I can’t show you how much space those image files take, because they are on the same folders as images contained in other catalogs, but a quick back-of-the-envelope assessment tells me it’s close to 3TB (terabytes) or 3,000GB.

The machine where I hold all of my digital photos is a fairly old iMac with a 3TB Fusion Drive. Until a few years ago, I kept everything, catalog and image files, on that disk, but as I kept adding more and more photos to my library, it became obvious that a 3TB disk was not going to be able to contain all of them.

Another consideration was that I wanted some form of redundant storage for the photos and I couldn’t have that inside the Mac, so I got myself an external unit, containing a pair of 4TB disks, that I configured as a RAID 1 mirrored array. What this means is that a copy of each file is stored on each of the two disks. Should one of the disks fail, the other one will still have the files.

I have other layers of backup, of course, but those are not relevant here.

After I got my external unit attached and configured, one night I moved all my image files from the internal disk to the RAID array and I was ready to go with the new setup.

What About the Catalogs?

My decision was to keep the catalogs on the internal disk.

The main reason for this was performance. Especially with a big catalog, it is important to keep it on a fast disk with a very fast connection to the CPU. I simply felt that a Fusion Drive, with its big solid-state cache, would have performed much better than an external drive.

When I finally upgrade my iMac to a more recent version, I will probably get one with a big SSD drive and store my catalogs there.

A consequence of this is that the catalogs themselves are not automatically mirrored and have to be backed up separately. I’m not going into a detailed explanation of my backup and restore strategies here. Suffice to say that the backup chain of my internal disk is separate from the backup chain of the external unit. If I lose one of the two, I can recover its contents separately and everything will still work.

Compared to other photographers, who have image libraries comprising millions of photos, I am a relatively low-volume shooter. If your numbers are comparable to mine, keeping the catalogs on the internal disk and the image files on an external one is a good compromise between performance and cost.

I recommend using a dual-disk external unit, as those can be had for a few hundred dollars and provide a first level of data redundancy that is the absolute minimum you should aim for.

If your needs are not satisfied by this kind of setup, you want to access your files from different devices on your home network, or even remotely, you should probably look into a NAS or SAN solutions like the ones made by companies like Drobo and Synology, but be prepared to spend much more.

Can I Put My Catalogs On a Network Drive?

In a word: no.

Lightroom catalogs only work properly when accessed from a single computer at a time and perform better when accessed over a fast, local connection bus.

One Catalog Or Multiple Catalogs?

The question about whether it is better to catalogue your photos in a single place or to use separate catalogs is as old as Lightroom itself.

Before Lightroom became a mature product (keep in mind that maturity for a software product is typically reached in 10 years from the first release) it was common wisdom that large catalogs were not performing well.

Is this still true nowadays?

I don’t have a good answer to that question, as I haven’t done any serious testing. All I can say is that, in recent years, I have started using a single catalog and haven’t noticed any significant slowdown as I keep adding more images to it.

In fact, if you look at the screenshot above, you’ll notice that the name of my main catalog refers to the year 2013. Before that, I would create one main catalog per year and then one more catalog for each trip I took or major event I attended. Now I don’t do that anymore.

The problem with having multiple catalogs is that each one is completely separated from the others. Indeed, when you switch to a different catalog within Lightroom, the whole application restarts itself.

Because of this, it’s impossible to do image searches that span multiple catalogs, compare images or copy settings across catalogs.

This is why I recommend that most people use a single catalog.

Again, I’m not a large volume shooter, so those who manage millions of photographs might come to different conclusions. Also, those who photograph events, like weddings, might find it easier to have a separate catalog for each event.

But if you are an amateur and don’t shoot millions of photos every year, I don’t think there are any good reasons to have more than one catalog.