[DRBD-user] drbd and LVM -> always getting duplicate volumes (was: can't use LVM2 on drbd devices)

[Carlos Xavier]

Hi.
To be able to use lvm on drbd devices i had to modify the file 
/etc/lvm/lvm.conf, to exclude the phisical devive and include the logical 
device.
This is what was modified:

    # By default we accept every block device:
#    filter = [ "a/.*/" ]
    filter = [ "r|/dev/cdrom|", "r|/dev/sda6|", "a|/dev/drbd0|", 
"r|/dev/sda7|", "a|/dev/drbd1|" ]

----- Original Message ----- 
From: "Tomasz Chmielewski" <mangoo at wpkg.org>
To: <drbd-user at linbit.com>
Sent: Monday, January 14, 2008 2:29 PM
Subject: [DRBD-user] drbd and LVM -> always getting duplicate volumes (was: 
can't use LVM2 on drbd devices)


> After a couple of days of struggling I got to the point where I have to 
> conclude that using LVM reliably over DRBD devices is impossible.
>
> As there are many users using LVM on DRBD, I would like to be corrected, 
> of course.
>
> Below, a step-by-step configuration of DRBD and LVM:
>
>
> 1. A relevant part of drbd.conf - our drbd0 device is on /dev/sda:
>
>     on san2 {
>         device    /dev/drbd0;
>         disk      /dev/sdb;
>         address   192.168.111.158:7789;
>         meta-disk internal;
>     }
>
>
> 2. Create drbd0 meta data:
>
> # drbdadm create-md r0
>
>
> 3. Start DRBD:
>
> # /etc/init.d/drbd start
>
>
> 4. Initial device sync:
>
> # drbdadm -- --overwrite-data-of-peer primary all
>
>
> 5. Now, we should be able to create LVM - pvcreate first:
>
> # pvcreate /dev/drbd0
>   Physical volume "/dev/drbd0" successfully created
>
>
> 6. Let's create a volume group - Houston, we have a problem!
>
> # vgcreate testvolume /dev/drbd0
>   Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/sdb not 
> /dev/drbd0
>   Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/drbd0 
> not /dev/sdb
>   Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/sdb not 
> /dev/drbd0
>   Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/drbd0 
> not /dev/sdb
>   Volume group "testvolume" successfully created
>
>
> 7. pvs confirms it - LVM sits on /dev/sdb, not on /dev/drbd0 - certainly, 
> nothing will be replicated by DRBD:
>
> # pvs
>   Found duplicate PV YIoJ98OFL3vhqhi7ek98UWkT7aBIzgrz: using /dev/sdb not 
> /dev/drbd0
>   PV         VG         Fmt  Attr PSize   PFree
>   /dev/sdb   testvolume lvm2 a-   558.57G 558.57G
>
>
>
> As device names are not necessarily persistent (if /dev/sdb is a iSCSI 
> drive, next time one boots it can be /dev/sdc) and a similar is for device 
> mapper devices (think of crypted devices), setting up filters in lvm.conf 
> will not be reliable.
>
> How can I use LVM over DRBD devices *reliably*?
>
>
>
> -- 
> Tomasz Chmielewski
> http://wpkg.org
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>