Unknown disk

[T.C. Zhao]

Hi, netfolks,

I really need your expertise and experience related the SGI machines 
to help me out.  Recently, the SGI(4D/210GVX) our group has got 
very sick(dead ?). The symtoms: 
1. When X software was started (to be exact, xcalc), lots
    of error message was printed (no space on device xxxxxx).
    I think xxxxxx is the device no. for the root or swap,
    I am not sure.
2.  Killed xcalc, and subsequently, the window manager
    is dead. After a while, (with some messages,
    like no root, no lp or something)  then boot menu comes up.
3.  Tried to start the system, it wont start:
    unknown disk.

To my very limited undstanding, the /root or swap disk was runing
low at the moment the X software was started(we are runing
IRIS 3.2.1 and have only exec-only X), thus causing the
crash. What I do not have a clue is why the window manager
was dead and how the disk became unknown. Most importantly,
how to prevent this to happen in the future. Before the
crash, whenver the system was rebooted, there were bad blocks,
and got automatically fixed and df always show different
disk usage before and after the reboot, sometime
more disk, sometime less. and I noticed that the lost+found
directory was growing, Shall I be alarmed ? Can I delete
whatever in lost+found ? Where the lost disk space go ? 
(before I stared X, i checked there was plenty disk space
in /root(more than a few meg), when I see the first error message,
disk was 100% used).

I hope we won't lose any data in other partitions other than root.

Thanks for any help.