Running the attached script results in:

• disk_usage.2 created in run #96 (~5 minutes runtime)
• disk_usage.3 created in run #375 (~17 minutes runtime)
• disk_usage.4 created in run #1009 (~44 minutes runtime)
• disk_usage.5 created in run #2276 (~99 minutes runtime)

The script is inserting roughly 20MB worth of 5000* byte strings in each run.

*actually 4990 to 5000 bytes, this appears to be significant as using fixed strings of 5000 bytes didn't cause this issue.

The rename appears to be significant - when I took it out I couldn't re-create this issue.

Attached the output of this script during my run as well as mongod.log.
Note that mongod.log times are in GMT however the output times are in AEST (GMT+11). Sorry about that.