PfSense unresponsive after a while but working in Virtualbox

[enedene]

I have pfsense (2.0, x64) installed on Virtualbox and use it on my home network to route traffic and for traffic shaper.
I had the thing running for 20days without any problems. I'm not sure if it's releated but couple of days ago I've configured traffic shaper for the first time and after a while I couldn't log into firewall through web interface
Here is the error in web interface that I get at log in:

"Warning: fopen(/tmp/config.lock): failed to open stream: Device not configured in /etc/inc/util.inc on line 123 Warning: flock() expects parameter 1 to be resource, null given in /etc/inc/util.inc on line 134 Warning: fclose(): supplied argument is not a valid stream resource in /etc/inc/util.inc on line 135 Warning: session_start(): open(/var/tmp//sess_e9566fd5e196d1d55f6e99f832ef02b1, O_RDWR) failed: No space left on device (28) in /etc/inc/auth.inc on line 1253"

I see this "No space left on device 28" I don't know if that has anything to do with disk size, but when it works it says that only 9% of disk is used, the same goes for shell command "df -h"
When I look at the console output I also can't do anything, even restart I just get error:

"unknown: TIMEOUT -READ_DMA retrying (1 retry left) LBA=10295343
g_vfs_done(): ad0s1a[WRITE[offset=15412594, length=16384)error = 6
Device ad0s1a went missing before all of the data could be written on it; expect data loss.
Device ad0s1a went missing before all of the data could be written to it; expect data loss.
vnode_pager_getpages: I/O read error
vm_fault: pager read error, pid 28860 (php)

[/quote]
I also see this when I go to command line interface:

/:create/symlink failed, no inodes free
/: write failed, filesystem is full
Fatal error: Unknown: apc_fcntl_lock failed: in Unknown on line 0

here is a df -h output:

Filesystem      Size     Used    Avail     Capacity       Mounted on
/dev/ad0s1a    5.8G    506M    4.8G       9%             /
devfs             1.0K     1.0K     0B          100%         /dev
/dev/md0       3.6M     34K      3.3M       1%            /var/run
devfs             1.0K     1.0K      0B         100%         /var/dhcp/dev

Btw, I did default install, gave installation to decide about partitioning.

Although these errors are here, firewall seems to be working fine, except that I can't get to web interface to configure anything. And when I restart a computer and go to RDP graphs, you see the hole in place when the web interface stopped working because of this error. So it seems that logging is stopped when this happens, although firewall works fine.

[enedene]

It seems that my physical drive has failed.