Question

space added not showing in redhat linux

Linux, Redhat Linux

added disk space , but not showing in physical volume as well in the logical volumes.

how can I check if the disk is there?

The simple way would be to run this command

dmesg

That command will run through a list of messages about hardware added/initialized. From there all you will need to do is figure out which hard drive you are using, and if you have not partitioned it, you can use the graphical tool, you can simply go do that (can't remember the GUI program's name). If you don't use a GUI, you can do this (in this example, I am assuming that the new harddrive showed up as "hdb":

fdisk /dev/hdb

If you need help from here, I reccomend you have a look at About.com's guilde to Fdisk
Now, you will need to mount the new drive. Most people think you need to mount the drive in /mnt/ but that is not true. You can mount it in /var/www/ /home/<user_folder>/ or whatever place you like, so long as the directory you are mounting it to is currently empty. You can either mount it each time, or simply edit your /etc/fstab file

vim /etc/fstab

my fstab looks something like this:

 # /etc/fstab: static file system information.
 #
 # <file system> <mount point>   <type>  <options>       <dump>  <pass>
 proc            /proc           proc    defaults        0       0
 # /dev/sda1
 UUID=<random gibberish>              ext3    defaults,errors=remount-ro 0       1
 # /dev/sda5
 UUID=<random gibberish> none            swap    sw              0       0
 /dev/scd0       /media/cdrom0   udf,iso9660 user,noauto,exec 0       0

I modified it slightly so you wouldn't see my harddrive info (serial number). I replaced it with <random gibberish>
to add a drive, you would add something like this to the bottom of your fstab:

 /dev/hdb1       /var/www        ext3    defaults        0       0
 

You see how the hdb changed to hdb1? Well, that's the new partition on the new drive. Each partition (be it 1, or 1000) gets a numeral at the end, starting with 1.
Rember, I've only been using hdb as an example. Yours may be different. It may be sda, sdb(those are SATA drives, usually). Just make sure you know which drive you are working with. If you get the wrong one, you could accidentally repartition your primary drive (I'm not sure if you actually can, but I'm covering my butt here).