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Old 12-08-2009, 05:07 PM
Peter Humphrey
 
Default Newcomer's question about existing software raid

Hello list,

I've just used the 9.10 standard installation CD to install Kubuntu in some
spare space on an IDE drive, and now I want to mount one of the existing
mdraid partitions on /home/<user>/common. I've googled for advice but I only
see how to install on a new mdraid partition, not how to mount one that's
there already.

I've installed mdraid, and the mdraid.conf file is written, apparently
correctly, but I still get "/dev/md2 does not exist" when I attempt to mount
it.

Would someone please point me to where I can find the right advice?

Thanks.

--
Rgds
Peter

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Old 12-08-2009, 05:28 PM
Patrick Doyle
 
Default Newcomer's question about existing software raid

On Tue, Dec 8, 2009 at 1:07 PM, Peter Humphrey <peter@humphrey.ukfsn.org> wrote:
> Hello list,
>
> I've just used the 9.10 standard installation CD to install Kubuntu in some
> spare space on an IDE drive, and now I want to mount one of the existing
> mdraid partitions on /home/<user>/common. I've googled for advice but I only
> see how to install on a new mdraid partition, not how to mount one that's
> there already.
>
> I've installed mdraid, and the mdraid.conf file is written, apparently
> correctly, but I still get "/dev/md2 does not exist" when I attempt to mount
> it.
>
> Would someone please point me to where I can find the right advice?
>
You could try looking at

http://www.linuxfoundation.org/collaborate/workgroups/linux-raid/raid_setup

I also recall reading various RAID documents in the Ubuntu user
contributions site.

In the mean time, what does:

$ cat /proc/mdstat

tell you?

--wpd

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Old 12-08-2009, 05:37 PM
Preston Hagar
 
Default Newcomer's question about existing software raid

On Tue, Dec 8, 2009 at 12:07 PM, Peter Humphrey
<peter@humphrey.ukfsn.org> wrote:
> Hello list,
>
> I've just used the 9.10 standard installation CD to install Kubuntu in some
> spare space on an IDE drive, and now I want to mount one of the existing
> mdraid partitions on /home/<user>/common. I've googled for advice but I only
> see how to install on a new mdraid partition, not how to mount one that's
> there already.
>
> I've installed mdraid, and the mdraid.conf file is written, apparently
> correctly, but I still get "/dev/md2 does not exist" when I attempt to mount
> it.
>
> Would someone please point me to where I can find the right advice?
>
> Thanks.
>
> --
> Rgds
> Peter
>

I would first try

cat /proc/mdstat

Does it show your RAID array? If so, it should let you know what it
is showing up as /dev/md1, /dev/md2, etc as well as the state of it
(Degraded, etc).

If it doesn't show your RAID array, there are a couple of things you can try:

mdadm --assemble --scan

will try to find and start any RAID arrays that are listed in the
mdadm.conf file (which is usually at /etc/mdadm/mdadm.conf)

After you run it

cat /proc/mdstat

again to see if it found the arrays. If not, you might try

mdadm --assemble /dev/md2 [partitions]

where [partitions] is replaced with the partitions that make up the
raid array (they should look something like /dev/sdc2 or /dev/hdb5,
etc depending on if you are using IDE or SATA drives and which drives
you set them up on)

If that still doesn't work, I would try one of these solutions from
the mdadm man page to figure out exactly which drives/partitions have
the RAID superblocks on them so you know how to issue the assemble
command:

echo ’DEVICE /dev/hd*[0-9] /dev/sd*[0-9]’ > mdadm.conf
mdadm --detail --scan >> mdadm.conf
This will create a prototype config file that describes
currently active arrays that are known to be
made from partitions of IDE or SCSI drives. This file should
be reviewed before being used as it may
contain unwanted detail.

echo ’DEVICE /dev/hd[a-z] /dev/sd*[a-z]’ > mdadm.conf
mdadm --examine --scan --config=mdadm.conf >> mdadm.conf
This will find arrays which could be assembled from
existing IDE and SCSI whole drives (not parti‐
tions), and store the information in the format of a config
file. This file is very likely to contain
unwanted detail, particularly the devices= entries. It
should be reviewed and edited before being
used as an actual config file.

mdadm --examine --brief --scan --config=partitions
mdadm -Ebsc partitions
Create a list of devices by reading /proc/partitions, scan
these for RAID superblocks, and printout a
brief listing of all that were found.


Hope this helps.

Preston

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Old 12-08-2009, 05:42 PM
Peter Humphrey
 
Default Newcomer's question about existing software raid

On Tuesday 08 December 2009 18:28:16 Patrick Doyle wrote:

> You could try looking at
>
> http://www.linuxfoundation.org/collaborate/workgroups/linux-raid/raid_setup

I'd missed that one - thanks.

Meanwhile, my system just needed one more reboot (that Kubuntu system and this
Gentoo one are on the same box). Everything's now working just fine.

Thanks for your help, Patrick, and sorry about the noise.

--
Rgds
Peter

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Old 12-08-2009, 05:47 PM
Peter Humphrey
 
Default Newcomer's question about existing software raid

On Tuesday 08 December 2009 18:37:32 Preston Hagar wrote:

> I would first try
>
> cat /proc/mdstat

It was empty at the time, but see my reply to Patrick, which has crossed yours
to me in the post

> If it doesn't show your RAID array, there are a couple of things you can
> try:
>
> mdadm --assemble --scan
[...]
> mdadm --assemble /dev/md2 [partitions]

They're already assembled and ready to go in this Gentoo system on the same
box.

> If that still doesn't work, I would try one of these solutions from
> the mdadm man page to figure out exactly which drives/partitions have
> the RAID superblocks on them so you know how to issue the assemble
> command:

Thanks for the detailed advice, but the raid setup was complete, Kubuntu
kernel just wasn't looking for it at boot time. It is now, so I'm relieved
not to have to go digging quite so deep :-)

> Hope this helps.

Indeed, and thanks again.

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Peter

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