CentOS - Nov 2005 - Rescan harddisk size without rebooting

Hi list,
I have a SAN attached to a CentOS 4.2 server. I have expanded the size 
of the virtual disk within the SAN (by adding a new HD to the disk pool) 
and need CentOS to see the new size (CentOS see it as /dev/sdb). I'm 
using LVM. Do you  know a method for the Volume Group to see that one of 
its harddisk is now bigger, without rebooting (it's not a problem with a 
reboot but since the LDAP directory is on this server, it is problematic).
Thanks.
kfx

On Wed, 2005-11-09 at 11:52 +0100, kadafax wrote:
> Hi list,
> I have a SAN attached to a CentOS 4.2 server. I have expanded the size 
> of the virtual disk within the SAN (by adding a new HD to the disk pool) 
> and need CentOS to see the new size (CentOS see it as /dev/sdb). I'm 
> using LVM. Do you  know a method for the Volume Group to see that one of 
> its harddisk is now bigger, without rebooting (it's not a problem with
a
> reboot but since the LDAP directory is on this server, it is problematic).
> Thanks.
Anytime you expand what Linux sees as a "physical device" -- even
though
it's a volume over a FC HBA -- that is not always easy to address.  You
typically have to rescan the SCSI bus (which is what the FC HBA presents
the storage as).  Unfortunately, if you have filesystems mounted on that
device, they may not update -- even if you're using LVM atop.

Last time I checked, there was no single command to rescan the SCSI bus
in RHEL.  Ironically enough, I typically just do a Google search for
"Linux SCSI bus scan" and run the few commands listed whenever I need
to
do so.  But I don't know what that might do to your running storage --
it could kill your mounts.

-- 
Bryan J. Smith     b.j.smith at ieee.org     http://thebs413.blogspot.com
----------------------------------------------------------------------
The best things in life are NOT free - which is why life is easiest if
you save all the bills until you can share them with the perfect woman

kadafax wrote:
> Hi list,
> I have a SAN attached to a CentOS 4.2 server. I have expanded the size 
> of the virtual disk within the SAN (by adding a new HD to the disk pool) 
> and need CentOS to see the new size (CentOS see it as /dev/sdb). I'm 
> using LVM. Do you  know a method for the Volume Group to see that one of 
> its harddisk is now bigger, without rebooting (it's not a problem with
a
> reboot but since the LDAP directory is on this server, it is problematic).
If you do "fdisk /dev/sdb", does it show you correct (new) size? 
Fdisk
should query device directly (and not relay on cached copy of partition 
table in kernel).  If yes, just extend partition where your physical 
volume is, save new partition table (fdisk will instruct kernel to 
re-read it), do pvresize, lvresize, and finally resize the file system 
(this can be done while file system is mounted at least for ext2 and 
ext3).  If your version of LVM reports that pvresize is non-functional 
(I believe pvresize was implemented relatively recently for LVM2), 
there's couple of "dirty" tricks how to resize physical volume.