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Date: Thu, 19 Mar 2009 21:55:07 -0500
From: Vu Pham <vu@sivell.com>
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Subject: Re: [linux-lvm] multipath question
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	<1237487053.26341.12.camel@chandra-ubuntu>
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To: sekharan@linux.vnet.ibm.com, LVM general discussion and development <linux-lvm@redhat.com>


Chandra Seetharaman wrote:
> On Thu, 2009-03-19 at 13:00 -0600, vu pham wrote:
>> I set up multipath on /dev/sda and /dev/sdb which are mapped from a 
>> remote single disk, which has two partitions.
>>
>> Below are some output.
>> [root@vm5 mpath]# ls -l
>> total 0
>> lrwxrwxrwx 1 root root 7 Mar 19 10:34 mpath0 -> ../dm-2
>> lrwxrwxrwx 1 root root 7 Mar 19 10:34 mpath0p1 -> ../dm-3
>> lrwxrwxrwx 1 root root 7 Mar 19 10:34 mpath0p2 -> ../dm-4
>>
>> [root@vm5 mpath]# multipath -ll
>> mpath0 (16465616462656166313a3100000000000000000000000000) dm-2 
>> IET,VIRTUAL-DISK
>> [size=5.0G][features=0][hwhandler=0]
>> \_ round-robin 0 [prio=0][active]
>>   \_ 0:0:0:1 sda 8:0   [active][ready]
>> \_ round-robin 0 [prio=0][enabled]
>>   \_ 1:0:0:1 sdb 8:16  [active][ready]
>> [root@vm5 mpath]#
>>
>>
>>  From the multipath command, I know dm-2 is mapped from two devices 
>> /dev/sda and /dev/sdb as expected.
>>
>> But how can I know if dm-3 is mapped from /dev/sda1 and /dev/sdb1, and 
>> dm-4 from /dev/sda2 and /dev/sdb2 ?
>>
>> The command "multipath -ll" only gives info on mpath0 or dm-2.
>>
>> I tried  multipath -ll /dev/mpath/mpath0p1 but does not show anything.
> 
> mpath0 is analogous to sda and mpath0p1, mpath0p2 are analogous to sda1,
> sda2.
> 
> since there is "mpath0" in mpath0p1 and mpath0p2, you can be sure that
> they are built off sda and sdb (in effect mpath0p1 is made of sda1 and
> sdb1 and so on)...
> 

Chandra, that makes sense. Thanks a lot for your explanation.

Vu