External storage can be compressed by about a factor of 20 by running the maintenance scripts `trackBlobs.php` and `recompressTracked.php`. There has been recently a space shortage on ES hosts (T105843), and that is going to be fixed short term in hardware, but investigation on software/operations should ensue.
Two important issues, however, must be fixed first:
* Record Flow references to ExternalStore in text T106363
* The script has been untested for years, and it should be checked before its execution (T106388, plus additional general testing)