performance - Will an SSD provide a noticeable benefit for Lightroom over a traditional harddrive?

I am a huge Lightroom (3.6) user, and have a 2006 2.15 Ghz Core 2 Duo 24" iMac, running Lion. This Mac it limited to 3GB RAM max, but does have dedicated graphics. I have about 50GB left on my harddrive. I have over 21,000 images in my LR catalog. The catalog itself is local on my iMac hard drive, but images are on attached storage.

My issue is that I have been having some noticeable performance issues with Lightroom. Dragging sliders can be jumpy at times, and sometimes switching modules has significant delays. I suspect that overhead in Lion is somewhat to blame, but it may also be all the files and apps on my Mac.

So, question is: does anyone have tested evidence of an SSD vs harddrive on Lightroom performance? How dependent is Mac OSX on free hard drive space when it pages to virtual memory? How much free space is preferred?

Or is my issue more related to LR itself, in that I have over 21,000 images in my LR catalog? Would I see noticeable improvement in the interface with a smaller catalog?

Trying to decide if the pain of opening my iMac and installing an SSD is worth it, or if I should instead save the $$ and put it toward an updated iMac in the future.

Answer

I recently got an SSD drive for my primary boot drive. It was a moderately fast one, with consistent 270mb/s read and write speeds. I've used lightroom with the catalog both on the SSD and on a normal HDD, and I did not see a whole lot of performance improvement for my catalog, which is about 12,000 photos or so.

As I started investigating how to improve the performance of Lightroom, I realized that the most significant factor that affected performance was the Camera RAW Cache size (Preferences -> File Handling -> Camera Raw Cache Settings -> Maximum Size). It defaults to 1Gb, however when working with a large number of RAW photos, a 1Gb cache is FAR, FAR too small. Increasing it to at least 20Gb offered good improvement, and increasing it to 50Gb offered considerable improvement. The improvement was a bit better on the SSD, however given the value of SSD space, I again moved the cache off onto a normal HDD. The performance gains are still evident, and I'm quite happy using LR with all of its data on a normal hard drive.

It should be noted that SSD's come in a very BROAD range of speeds and capabilities. Some are fairly slow relative to an HDD (which can usually offer around 60mb/s burst rates), where as some are insanely fast. SSD burst rates can range from as low as around 100mb/s or even lower for really cheap drives, to as high as 700mb/s or even more for highly specialized designs...such as those that fit into a PCI-E slot. Some SSD's include built-in high-speed secondary caches, some have better data distribution algorithms that optimize read or write speeds, etc. All these factors can affect whether an SSD might show a significant improvement for Lightroom performance or not. Lightroom generally stores the working image in memory, so if you are worried about single-image development speed, an SSD is not going to help much. The performance gains that can be realized from faster storage drive speeds happen when moving between files, performing multi-file operations, etc. The bottom line is...the more money you are willing to spend for better SSD technology and faster burst rate, the more likely you are to see an improvement.