[Linux-cluster] LVM and Multipath with EMC PowerPath (Was: CLVMD - Do I need it)

Roger Peña Escobio orkcu at yahoo.com
Sat Sep 23 21:16:13 UTC 2006

--- "Celso K. Webber" <celso at webbertek.com.br> wrote:

> Hello all,
> After reading a thread on this list (CLVMD - Do I
> need it), I started 
> playing around with CLVM, just to make sure two
> problems I had in the 
> past were solved:
> 1) LVM normally cannot be used on shared disks,

> 2) The other problem is not directly related to
> CLVM, but I found no 
> solution for it (yet). In my setup, I have multiple
> paths to the same 
> devices in the shared storage (either in a SAN or
> DAS). Under the EMC 
> solution, we employ PowerPath to solve the multiple
> devices issue for 
> each LUN. It works quite well. But LVM is not aware
> of PowerPath's 
> multiple path aggregation, so when it scans the PVs
> on the LUN's 
> partitions, it "finds" duplicates for the PVs, like
> this:

tyhe solution for this is to "filter" the
"under-powerpath devices" :-)
I mean, to filter to not scan the devices exported by
the SAN or DAS, and just use the powerpath devices for
the LVM
check the file /etc/lvm/lvm.conf

> Another matter is that using the /dev/emcpowerX
> devices I have also load 
> balancing, so even if LVM2 did failover to the other
> paths (the other 
> devices), I would loose the load balancing feature I
> can achieve with 
> PowerPath.

if you put LVM over powerpath, you are layering the
environment, do you?
path load balancing and failover are cover by
powerpath, and  LVM do its own business :-)

> Question 2: is there a way to "force" which devices
> LVM should employ 
> when scanning the PVs over the disks Linux
> recognize?

# A filter that tells LVM2 to only use a restricted
set of devices.
# The filter consists of an array of regular
expressions.  These
# expressions can be delimited by a character of your
choice, and
# prefixed with either an 'a' (for accept) or 'r' (for
# The first expression found to match a device name
determines if
# the device will be accepted or rejected (ignored). 
Devices that
# don't match any patterns are accepted.


RedHat Certified Engineer ( RHCE )
Cisco Certified Network Associate ( CCNA )

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