About swap_pager I/O error

[L'oiseau de mer]

My FreeBSD Machine sometimes appear these messages:
swap_pager: I/O error - pageout failed; blkno 2097158,size 4096, error
6 (or error 11)
swap_pager: I/O error - pageout failed; blkno 1048581,size 4096, error 6
swap_pager: I/O error - pageout failed; blkno 2097167,size 8192, error 6
...

This error messages often destroy some normal process or demond.
If not do reboot my system, i don't know how to deal with this problem.

our work is dump/restore these systems, and the methode that
add/remove these new disk
is "camcontrol rescan all". But i don't know whether it is this reason
that device not configured or not.