We are going to move image serving from ms1 (plus a few other miscellaneous things that also live on that host) to the new much bigger ms7 starting at 1 pm EST, 9 pm UTC.
We expect 30 to 60 minutes of down time (= no uploads of media files). Depending on how things go, reads of pages may be spotty as well during this time.
Any questions or comments, I'm in the #wikimedia-tech irc channel.
Ariel Glenn