Runtime error: could not open segment 1 of relation ...

This morning one of our production servers (8.1.1, Linux) threw a number of errors like these (different final number; first two [1663/43801] are all the same]:

2006-09-26 10:02:15.124 PDT 1387333718 ERROR: could not open segment 1 of relation 1663/43801/7274801 (target block 478216192): No such file or directory
2006-09-26 10:02:52.991 PDT 1387340456 ERROR: could not open segment 1 of relation 1663/43801/7274801 (target block 478216192): No such file or directory
2006-09-26 10:02:53.002 PDT 1387340458 ERROR: could not open segment 1 of relation 1663/43801/7274801 (target block 478216192): No such file or directory

The server never really recovered -- it kept running but was horribly slow. Rebooting seems to have cured the problem, but I am wondering what I made look into, etc.

The server in question is really a read-only beast with several hundred connections, typically, 4 gigs of RAM, and has not misbehaved before.

Any suggestions would be welcome! (Although I fear I know the answer -- disk issues.)

Thanks,

Greg Williamson
DBA
GlobeXplorer LLC