Hi Celine.
Generally when a server runs out of disk memory unexpectedly like that it's because the system has been on its feet for a long time, and meanwhile some application with an aggressive logging behavior has eventually filled the disk.
While you say you've added additional storage, are you sure the new space is available to /home? If so, I would try renaming 'pg_xlog/xlogtemp.12017' (i.e. mv pg_xlog/xlogtemp.12017 pg_xlog/xlogtemp.12017.OLD), then reboot and see if things come back online. It's possible some aspect of the last_used log file is corrupted now, and Arc-something-or-other is trying to access it and crashing when it fails to open it. Maybe removing that file from scope will force it to start over, clean.
I don't recall what that service name is or what it might be, and unfortunately I'm not in a position to check. But, in the terminal, you might try typing "service p", then hit tab two times fast, and see if CentOS will suggest a bunch of known service names that start with "p" ..if there are multiple service entries that look "postgres-like" (one might say "postgresque.. ..sorry I realize this is no place for a joke :/) then try stopping and restarting each of those services. Do a full service stop, then fresh service start just in case.
The next thing I would try would be clearing out the entire log directory (pg_xlog), just in case there is a related log that got hosed. If your organization looks down on deleting logs, copy them into a safe directory before eliminating them so that you'll have copies. Another thing worth considering, if free space in your /home directory is still an issue, deleting one or two recent log files probably won't help. You might need to figure out what happened to all your space and free some up relative to /home. It might be enough just to find and eliminate the largest and/or oldest logs. I would aim to free up at least a gig to give you some headroom. Then once you've done the spring cleaning, reboot and see if the system comes back up.
Hopefully it doesn't come down to uninstalling and reinstalling DataStore, entirely, as someone else mentioned. That seems like an awfully heavy-handed solution. (Although, unfortunately, it wouldn't surprise me since it came from the same organization that tightly couple's the system's FQDN to the software at install-time ..an absolutely terrible design decision, IMO.)
Anyway, I apologize this isn't more helpful. May the odds be ever in your favor.
/Elijah
