I have a similarly-configured VPS and modified the /dev/vzfs entry in /etc/fstab
in order to get quota
to work. The full contents of this file are:
proc /proc proc defaults 0 0
none /dev/pts devpts rw 0 0
/dev/vzfs / reiserfs rw,usrquota,grpquota 0 0
Obviously, don't copy-paste the last line verbatim if your system uses a different device name/path.
And use caution when modifying this file; mistakes can render your system un-bootable and your only option will be to start from scratch.
If your provider offers a "snapshot" style backup service, it would be worth paying for it, even if only while you're configuring the server. Most providers will prorate those "add-on" services, too, so you may be able to pay just a few bucks for two or three days of access to the backup service.