[linux-lvm] Disk /dev/dm-0 doesn't contain a valid partition table

[Sean McGlynn]

Bryn,

Thank you for taking the time to reply.

I'm glad to see this is not an issue. 

As for "dev253," if I only have three physical devices, why four dm entries?

Thanks again.


----- Original Message ----
From: Bryn M. Reeves <breeves at redhat.com>
To: LVM general discussion and development <linux-lvm at redhat.com>
Sent: Monday, May 21, 2007 10:28:35 AM
Subject: Re: [linux-lvm] Disk /dev/dm-0 doesn't contain a valid partition table


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Sean McGlynn wrote:
> Hello,
> 
>  
> 
> I did an fdisk -l to review my partition table (see results below), and
> found four entries that end with "Disk /dev/dm-X doesn't contain a valid
> partition table."  I don't recall seeing this in the past, so I believe
> it is something new.

Later kernels include dm devices in the list of partitions in proc, so
fdisk will attempt to scan them for partition tables. It's not harmful,
just noise.

> I recently began using kernel 2.6.21.1, up from 2.6.9-42.  I don't know
> if perhaps this had some effect, or if the entries are normal and I just
> never noticed them.

If you don't like it & you've not configured anything to use /dev/dm-*
devices directly (instead of /dev/mapper/* or /dev/<volgroup>/* or
whatever) then you can reconfigure udev to not create the dm-* nodes.

- From memory, you need to comment out the rule that begins
"KERNEL="dm-[0-9]*" in /etc/udev/rules.d/50-udev.rules, or, for newer
udevs you can add ignore_device:

KERNEL=="dm-[0-9]*", ACTION=="add", OPTIONS+="ignore_device"

>  
> 
> What led me here is that sar -d output includes four entries for hard
> drives (dev253 entries) when there are only three on my system.  Fdisk
> is reporting four DM devices, so I'm thinking there is some correlation,
> but I don't know what.

Those "dev253" entries are your device-mapper devices. Take a look at
/dev/dm-* with ls -l and you will see that the major number is 253.

Kind regards,
Bryn.

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