Originally Posted By: ryck
When I saw that the enable/disable button wasn't even functional, I wondered if Disk Utility might itself be faulty

You cannot disable journaling on the boot volume or on your Time Machine volume. That's why the button would be disabled for such volumes.

But as mentioned by others, journaling has nothing to do with Spotlight. Journaling is insurance for the files that make up your directory. What may seem to the user to be a single simple change (for example, renaming a file) may actually be a whole series of updates to the directory (delete the old file while remembering its location on disk and other metadata, then create a file with the new name but referring to the old location and metadata. If adding the new name requires splitting a block in the B*tree in the file catalog, a new block has to be taken from the free blocks list, information needs to be copied to it to turn one over-full block into two half-full blocks, the new block has to be linked in, and the free blocks list needs to be updated. etc.)

The danger is that your computer may fail right in the middle of that (loss of power, system fault, etc.), leaving the catalog in very bad shape. To counter that, all the changes are written to the journal first, then applied to the catalog. If the computer crashes, it can check the journal when it comes back up to see what, if anything, it was in the middle of when it crashed, and can finish the job.

The useful lifetime of information in the journal is measured in seconds at most. Indeed, the journal is only actually read from when recovering from a crash. It never needs to be "rebuilt".