storage sync failed on magnetic disk: Input/output error

Noticed this in one of my pg logs last Friday:

LOG:  could not fsync segment 0 of relation 1663/16387/22359: Input/output error
ERROR:  storage sync failed on magnetic disk: Input/output error

This relation corresponds to a table, which receives thousands of inserts via
COPY every couple of minutes. I've not noticed that message before now, nor
since then.

# select version();
PostgreSQL 8.1beta3 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.3.5
(Debian 1:3.3.5-13)

uname -a
Linux dev12 2.6.11-1-686-smp #1 SMP Mon Jun 20 20:18:45 MDT 2005 i686 GNU/Linux

6 disk SCSI, hardware RAID 5

Any ideas on what could have caused this etc?

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