Can anybody help me. How can I retreive a data from my old unix SCSI hdd. My server is having a new SCSI Hdd. What should I do. Somebody was telling to mount the old hdd and take. What should I do to mount this
old hdd and copy the data.

Rajesh,
Tata Coffee Ltd

What do you want to do? Copy the whole rootdisk? Just retrieve some data? Do you already boot from the new disk? Is an OS installed?
Did the old disk work?

I guess the new disk is bigger, faster, more colorful, you already installed *n*x on it, it is recognized as /dev/scda and the old Disk is attached to your system and mounted on /dev/scdb?

Let me further assume that you just want to copy some data, that was on, let's say /export/home, which was a mount of partitition 2 of your old Disk?

What you would do is (for instance):
# mount /dev/scdb2 /mnt

then you can just copy the files you want (or use something like "(cd olddir && tar cf . - ) | (cd newdir && tar xf -)")

Assuming that you are referring to the same machine as your other post:
You can use Microlite Edge (Home of Microlite BackupEDGE / RecoverEDGE) to backup the old hard drive to tape, and restore it to the new disk.