The USB disk on S12 died over the weekend.  The rsyncs of s12 from barolo started to fail, and then upon logging into s12 found that the sda disk no longer showed up in lsusb.  So it looks like the disk has just died.  I have changed vertex.xml to comment out the <mount> element, and instead created a link from /media/usbdisk/projects to /home/daq/data/projects, so now the raw archive files are being written to the home partition:

daq@s12:~/isfs/projects/VERTEX/ISFS/config$ lsu
Filesystem      Size  Used Avail Use% Mounted on
/dev/mmcblk0p2  856M  2.4M  793M   1% /home
total 780
-r--r--r-- 1 daq eol 795677 Sep 26 23:01 s12_20160926_225143.dat

With almost 800M available and writing 54M per 12 hours, that means there is room for 7 days of data.  If I change the rsync configuration to remove more data and only leave the most recent 2 days of data at the site, then S12 could be offline for almost 5 days before it starts losing data.  So maybe you'd prefer to go without a new USB disk, it certainly seems feasible.

If you choose to replace it with another 8GB disk, then once you insert it, it can be formatted remotely on the DSM, and then the configuration needs to be switched back to using the mount option.