Solaris

Yes, We have backed up our data, but not OS.
We are sure, OS dont responce iostat -En command. Output is below.

server1:{127}% iostat -En
Usage: iostat [-tdDxcI] [-l n] [disk ...] [interval [count]]

uname -a output is below

server1:{128}% uname -a
SunOS server1 5.5.1 Generic_103640-27 sun4u sparc SUNW,Ultra-2


We are still receiving same errors. And /var/adm/messages file is growing. This file's size is 30 MB. Is this status dangerous? Should I delete this file?
In addition, OS is very slow. It reply very late and open tools very slow. Is it normal?
We have tape backup.
Thanks.

omg.. brother.. its getting serious, dun delete messages file, you may clear its contents for now "cat /dev/null > /var/adm/messages.
Stop accessing the system for any further I/O activities.
Get a replacement disk - same part-number
Restore data which is residing on the failed disk from tape (Serial Number: 0030V0KX4A )
installboot bootblk on slice 0 to make it bootable
shutdown the system.
insert new disk replacing the faulty one
power on the system for boot up