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;
firsttwo [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,
butI 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
notmisbehaved before. 

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

Thanks,

Greg Williamson
DBA
GlobeXplorer LLC