Added inode data to disk_usage. The other day I got:
Filesystem            Size  Used Avail Use% Mounted on
/dev/xvda1            7.9G  5.6G  1.9G  75% /
udev                  821M  4.0K  821M   1% /dev
tmpfs                 332M  164K  332M   1% /run
none                  5.0M     0  5.0M   0% /run/lock
none                  829M     0  829M   0% /run/shm
/dev/xvdb             147G   45G   95G  32% /mnt

Yet whe I tried to

$ sudo touch /mnt/test
touch: cannot touch `/mnt/test': No space left on device

So checking

Filesystem            Inodes   IUsed   IFree IUse% Mounted on
/dev/xvda1              512K    187K    326K   37% /
udev                    206K     382    205K    1% /dev
tmpfs                   208K     253    207K    1% /run
none                    208K       1    208K    1% /run/lock
none                    208K       1    208K    1% /run/shm
/dev/xvdb               9.4M    9.4M       0  100% /mnt

Hence

>>> rpc_proxy.sysinfo.sysInfo()

        {u'cpu_percent': 3.0,
         u'cpu_times': {u'idle': 4105971.75,
                        u'nice': 0.0,
                        u'system': 55322.1,
                        u'user': 92921.92},
         u'disk_partitions': [{u'disk_usage': {u'free': 309265399808.0,
                                               u'percent': 69.0,
                                               u'total': 999345127424.0,
                                               u'used': 689817583616.0
                                               u'iprecent': 7.0,
                                               u'ifree': 491028,
                                               u'inodes': 524288},
                               u'partition_info': {u'device': u'/dev/disk0s2',
                                                   u'mountpoint': u'/'}}],
         u'phymem_usage': {u'free': 44892160,
                           u'percent': 73.5,
                           u'total': 4294967296,
                           u'used': 4240707584}}