Storage space partition

[Allen, Jack]

-----Original Message-----
From: redhat-install-list-bounces at redhat.com
[mailto:redhat-install-list-bounces at redhat.com] On Behalf Of Bob McClure Jr
Sent: Friday, April 14, 2006 4:59 PM
To: Getting started with Red Hat Linux
Subject: Re: Storage space partition


On Fri, Apr 14, 2006 at 04:35:38PM -0400, Allen, Jack wrote:
> 
> 
> 	When using a SAN and there are multiple paths to it, you will see
> multiple sdX entries for the true storage. This means you could access
> /dev/sda and see the exact same things if you access /dev/sdb as an
example
> if the SAN had been configure to allow access to 1 LUN. With EMC's
> Navisphere and PowerPath installed, there will also be a /dev/emcpowera.
> This is what you want to either partition and or make the whole things a
> Physical Volume in LVM. When you run the pvcreate command, or many of the
> other LVM related command it scans the /dev directory and reads each block
> device it find to see if it is part of a Volume Group and/or can be used
by
> LVM. This is why you are getting the duplicate messages and the message
> about the cdrom.
> 
> 	To keep this from happening you have to edit /etc/lvm/lvm.conf.
> There are some pretty good comments that explains things. The main idea is
> to exclude the /dev/sd* and /dev/cdrom names and only use the
/dev/emcpower*
> names.

Why would you prefer to use /dev/emcpower* rather than /dev/sd*?
Seems the latter would yield fewer surprises, even if it's exactly
equivalent.  Just curious.
@@@@@@@@@@
Because if you use the /dev/dsb/sda and that path becomes inaccessible you
will not be able to use the disk. This is the whole purpose of EMC's
PowerPath. The /dev/emcpower* are pseudo devices and the software will
determine which path can be used. The PowerPath software also does load
balancing between the path. There can be many more than 2 paths. You could
have 2 FC HBAs that each are connected to a FC Switch, then each FC Switch
has 2 paths to the SAN, 2 for each SAN SP (Storage Processor). This would
give 4 paths to each LUN. So if the SAN has presented 4 LUNs the system
would see 16 /dev/sd* entries and the PowerPath software would create
/dev/emcpowera through /dev/emcpowerd. This would hold true even if the
/dev/sd* started at say /dev/sdc.
@@@@@@@@@

> 	This is a little brief in the scheme of things, but I hope it helps.
> I can try to give more detail if needed.
> 
> Talk 2 U later.
> Jack Allen

Cheers,
-- 
Bob McClure, Jr.             Bobcat Open Systems, Inc.
bob at bobcatos.com             http://www.bobcatos.com
The best things in life aren't things.

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See answers and comments above between @@@@@@@@@@.

Talk 2 U later.
Jack Allen