/dev/md* Device Files

/dev/md* Device Files

[Steve Witt]

I'm installing a software raid system on a new server that I've just 
installed Debian 3.1 (sarge) on. It will be a raid5 on 5 IDE disks using 
mdadm. I'm trying to create the array with 'mdadm --create /dev/md0 ...' 
and am getting an error: 'mdadm: error opening /dev/md0: No such file or 
directory'. There are no /dev/md* devices in /dev at the present time. I 
do have the md and raid5 kernel modules loaded. My question is: how do the 
/dev/md* files get created? Are they normal device file that are created 
with MAKEDEV?

Thanks...

Re: /dev/md* Device Files

[Gordon Henderson]

On Tue, 25 Jan 2005, Steve Witt wrote:

> I'm installing a software raid system on a new server that I've just
> installed Debian 3.1 (sarge) on. It will be a raid5 on 5 IDE disks using
> mdadm. I'm trying to create the array with 'mdadm --create /dev/md0 ...'
> and am getting an error: 'mdadm: error opening /dev/md0: No such file or
> directory'. There are no /dev/md* devices in /dev at the present time. I
> do have the md and raid5 kernel modules loaded. My question is: how do the
> /dev/md* files get created? Are they normal device file that are created
> with MAKEDEV?

It's odd that they aren't there - they are with Debian 3.0, and have
remained there when I've upgraded a few test servers to testing/Sarge.

	# cd /dev
	# ./MAKEDEV md

should do the business.

Gordon

Re: /dev/md* Device Files

[Andrew Walrond]

On Wednesday 26 January 2005 07:28, Gordon Henderson wrote:
> On Tue, 25 Jan 2005, Steve Witt wrote:
> > I'm installing a software raid system on a new server that I've just
> > installed Debian 3.1 (sarge) on. It will be a raid5 on 5 IDE disks using
> > mdadm. I'm trying to create the array with 'mdadm --create /dev/md0 ...'
> > and am getting an error: 'mdadm: error opening /dev/md0: No such file or
> > directory'. There are no /dev/md* devices in /dev at the present time. I
> > do have the md and raid5 kernel modules loaded. My question is: how do
> > the /dev/md* files get created? Are they normal device file that are
> > created with MAKEDEV?
>
> It's odd that they aren't there - they are with Debian 3.0, and have
> remained there when I've upgraded a few test servers to testing/Sarge.
>
>  # cd /dev
>  # ./MAKEDEV md
>
> should do the business.
>

A useful trick I discovered yesterday: Add --auto to your mdadm commandline 
and it will create the device for you if it is missing :)

Andrew Walrond

Re: /dev/md* Device Files

[Steve Witt]

On Wed, 26 Jan 2005, Andrew Walrond wrote:

> On Wednesday 26 January 2005 07:28, Gordon Henderson wrote:
>> On Tue, 25 Jan 2005, Steve Witt wrote:
>>> I'm installing a software raid system on a new server that I've just
>>> installed Debian 3.1 (sarge) on. It will be a raid5 on 5 IDE disks using
>>> mdadm. I'm trying to create the array with 'mdadm --create /dev/md0 ...'
>>> and am getting an error: 'mdadm: error opening /dev/md0: No such file or
>>> directory'. There are no /dev/md* devices in /dev at the present time. I
>>> do have the md and raid5 kernel modules loaded. My question is: how do
>>> the /dev/md* files get created? Are they normal device file that are
>>> created with MAKEDEV?
>>
>> It's odd that they aren't there - they are with Debian 3.0, and have
>> remained there when I've upgraded a few test servers to testing/Sarge.
>>
>>  # cd /dev
>>  # ./MAKEDEV md
>>
>> should do the business.
>>
>
> A useful trick I discovered yesterday: Add --auto to your mdadm commandline
> and it will create the device for you if it is missing :)
>

Well, it seems that this machine is using the udev scheme for managing 
device files. I didn't realize this as udev is new to me, but I probably 
should have mentioned the kernel version (2.6.8) I was using. So I need to 
research udev and how one causes devices to be created, etc.

Thanks for the help!!

RE: /dev/md* Device Files

[J. Ryan Earl]

Did you have the md module inserted into the kernel at this point?  It
should automatically the md device entries for you, at least it does with
udev-045.

-ryan

-----Original Message-----
From: linux-raid-owner@vger.kernel.org
[mailto:linux-raid-owner@vger.kernel.org]On Behalf Of Steve Witt
Sent: Tuesday, January 25, 2005 4:54 PM
To: linux-raid@vger.kernel.org
Subject: /dev/md* Device Files


I'm installing a software raid system on a new server that I've just
installed Debian 3.1 (sarge) on. It will be a raid5 on 5 IDE disks using
mdadm. I'm trying to create the array with 'mdadm --create /dev/md0 ...'
and am getting an error: 'mdadm: error opening /dev/md0: No such file or
directory'. There are no /dev/md* devices in /dev at the present time. I
do have the md and raid5 kernel modules loaded. My question is: how do the
/dev/md* files get created? Are they normal device file that are created
with MAKEDEV?

Thanks...

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Re: /dev/md* Device Files

[Neil Brown]

On Wednesday January 26, sawitt@electra.rsc.raytheon.com wrote:
> > A useful trick I discovered yesterday: Add --auto to your mdadm commandline
> > and it will create the device for you if it is missing :)
> >
> 
> Well, it seems that this machine is using the udev scheme for managing 
> device files. I didn't realize this as udev is new to me, but I probably 
> should have mentioned the kernel version (2.6.8) I was using. So I need to 
> research udev and how one causes devices to be created, etc.

Beware.... udev has an understanding of how device files are meant to
work which is quite different from how md actually works.

udev thinks that devices should appear in /dev after the device is
actually known to exist in the kernel.  md needs a device to exist in
/dev before the kernel can be told that it exists.

This is one of the reasons that --auto was added to mdadm - to bypass
udev.

NeilBrown

Re: /dev/md* Device Files

[Mike Hardy]

Q: How do you make devices persistent in udev, so they stop getting 
created dynamically?

A: you can cd into /dev/ and ./MAKEDEV md, then cp /etc/md* to 
/etc/udev/devices/

then they'll reappear on boot. I wasted some time on this prior (I have 
a hot-swappable ide/cdrom drive and cd-burning stopped working when I 
went from RH9 to FC3, thanks udev!)

Works for me, anyway. Hope it helps

-Mike

Steve Witt wrote:
> On Wed, 26 Jan 2005, Andrew Walrond wrote:
> 
>> On Wednesday 26 January 2005 07:28, Gordon Henderson wrote:
>>
>>> On Tue, 25 Jan 2005, Steve Witt wrote:
>>>
>>>> I'm installing a software raid system on a new server that I've just
>>>> installed Debian 3.1 (sarge) on. It will be a raid5 on 5 IDE disks 
>>>> using
>>>> mdadm. I'm trying to create the array with 'mdadm --create /dev/md0 
>>>> ...'
>>>> and am getting an error: 'mdadm: error opening /dev/md0: No such 
>>>> file or
>>>> directory'. There are no /dev/md* devices in /dev at the present 
>>>> time. I
>>>> do have the md and raid5 kernel modules loaded. My question is: how do
>>>> the /dev/md* files get created? Are they normal device file that are
>>>> created with MAKEDEV?
>>>
>>>
>>> It's odd that they aren't there - they are with Debian 3.0, and have
>>> remained there when I've upgraded a few test servers to testing/Sarge.
>>>
>>>  # cd /dev
>>>  # ./MAKEDEV md
>>>
>>> should do the business.
>>>
>>
>> A useful trick I discovered yesterday: Add --auto to your mdadm 
>> commandline
>> and it will create the device for you if it is missing :)
>>
> 
> Well, it seems that this machine is using the udev scheme for managing 
> device files. I didn't realize this as udev is new to me, but I probably 
> should have mentioned the kernel version (2.6.8) I was using. So I need 
> to research udev and how one causes devices to be created, etc.
> 
> Thanks for the help!!
> 
> 
> -
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