After updating my X5L to a fairly recent build (16083, I believe) I began experiencing the following problems:
Database updating took a very long (sometimes upwards of an hour) and playback of MP3 files (I only use MP3s, so I can't comment on other file types) often took a long time to start, sometimes as long as several minutes or would fail to start at all.
Once started, playback would intermittently pause for several seconds, play for a while (maybe 2 to 30 seconds), then get "stuck" again for several seconds or occasionally forever, play for a little while, get stuck again, etc. Â Skipping to the next song would generally cause the intermittent playback to become worse and worse until I was forced to reboot the X5L. Â If I checked out the buffering threads in the debug menu during playback, I found they'd get partially full, then starve back to 0 for a while, fill partially again, etc.
After much fooling around with anti-skipping buffer length, directory caching, database RAM caching, chkdsk runs, etc., I found a solution to this problem that seems to have completely solved it, so I am posting here to try to save anyone else with a similar problem my frustration:
I had all (3300 or so, totalling around 13GB) of my MP3 files in one directory ("\MUSIC") on the root of my player's hard drive. Â Reorganizing this directory to place all of my files in a series of subdirectories, none of which contain more than a couple hundred files, reduced my Database update time down to just a couple minutes and once again enabled flawless playback.
I already had my player set to allow 10000 files per directory, so this was not the problem, but it seems the latest versions of Rockbox on the X5L are not happy with thousands of files in a single directory.