transferring RAID-1 drives via sneakernet

transferring RAID-1 drives via sneakernet

[Jeff Breidenbach]

I'm planning to take some RAID-1 drives out of an old machine
and plop them into a new machine. Hoping that mdadm assemble
will magically work. There's no reason it shouldn't work. Right?

old  [ mdadm v1.9.0 / kernel 2.6.17 / Debian Etch / x86-64 ]
new [ mdad v2.6.2 / kernel 2.6.22 / Ubuntu 7.10 server ]

Re: transferring RAID-1 drives via sneakernet

[David Greaves]

Jeff Breidenbach wrote:
> I'm planning to take some RAID-1 drives out of an old machine
> and plop them into a new machine. Hoping that mdadm assemble
> will magically work. There's no reason it shouldn't work. Right?
> 
> old  [ mdadm v1.9.0 / kernel 2.6.17 / Debian Etch / x86-64 ]
> new [ mdad v2.6.2 / kernel 2.6.22 / Ubuntu 7.10 server ]

I've done it several times.

Does the new machine have a RAID array already?

David

Re: transferring RAID-1 drives via sneakernet

[Jeff Breidenbach]

> Does the new machine have a RAID array already?

Yes.. the new machine already has on RAID array.
After sneakernet it should have two RAID arrays. Is
there a gotcha?

Re: transferring RAID-1 drives via sneakernet

[Brendan Conoboy]

Jeff Breidenbach wrote:
>> Does the new machine have a RAID array already?
> 
> Yes.. the new machine already has on RAID array.
> After sneakernet it should have two RAID arrays. Is
> there a gotcha?

It's not a RAID issue, but make sure you don't have any duplicate volume 
names.  According to Murphy's Law, if there are two / volumes, the wrong 
one will be chosen upon your next reboot.

-- 
Brendan Conoboy / Red Hat, Inc. / blc@redhat.com

Re: transferring RAID-1 drives via sneakernet

[Jeff Breidenbach]

> It's not a RAID issue, but make sure you don't have any duplicate volume
> names.  According to Murphy's Law, if there are two / volumes, the wrong
> one will be chosen upon your next reboot.

Thanks for the tip. Since I'm not using volumes or LVM at all, I should be
safe from this particular problem.

Re: transferring RAID-1 drives via sneakernet

[Michael Tokarev]

Jeff Breidenbach wrote:
>> It's not a RAID issue, but make sure you don't have any duplicate volume
>> names.  According to Murphy's Law, if there are two / volumes, the wrong
>> one will be chosen upon your next reboot.
> 
> Thanks for the tip. Since I'm not using volumes or LVM at all, I should be
> safe from this particular problem.

If you don't use names, you use numbers - like md0, md10 etc.
The numbers, as they now ARE names, should be different too.

There's more to this topic, much more.

There are different ways to start (assemble) the arrays.  I know at
least 4 - kernel autodetection, mdadm with mdadm.conf listed some
devices, mdadm with "empty" mdadm.conf and with using of 'homehost'
parameter (assemble all "our" arrays), and mdrun utility.  Also,
some arrays may be assembled during initrd/initramfs stage, and some
after...

The best is either mdadm with something in mdadm.conf, or mdadm with
homehost.  Note that neither of these ways, your "foreign" array(s)
will be assembled, and you will have to do it manually - wich is much
better than to screw things up trying to mix-n-match pieces of the
two systems.  You'll just have to figure the device numbers of your
"foreign" disks and issue an appropriate command, like this:

  mdadm --assemble /dev/md10 /dev/sdc1 /dev/sdd1 ...

using not yet taken mdN number and the right device nodes for your
disks/partitions.

If you want to keep the disks here, you can add the array info into
mdadm.conf or refresh superblock to have new homehost.

But if you're using kernel autodetection or mdrun... well, I for
one can't help here, -- your arrays will be numbered/renumbered
by a chance...

/mjt

Re: transferring RAID-1 drives via sneakernet

[David Greaves]

Jeff Breidenbach wrote:
>> It's not a RAID issue, but make sure you don't have any duplicate volume
>> names.  According to Murphy's Law, if there are two / volumes, the wrong
>> one will be chosen upon your next reboot.
> 
> Thanks for the tip. Since I'm not using volumes or LVM at all, I should be
> safe from this particular problem.

Volumes is being used as a generic term here.

You would be safest if, for the disks/partitions you are transferring, you made
the partition type 0x83 (linux) instead of 0xfd to prevent the kernel autodetecting.

Otherwise there is a risk that /dev/md0 and /dev/md1 will be transposed.

Having done that you can manually assemble the array and then configure
mdadm.conf to associate the UUID with the correct md device.

David

Re: transferring RAID-1 drives via sneakernet

[Jeff Breidenbach]

I just finished the transfer and it went great. Thanks for all
the advice. I went with the assemble-by-uuid approach in
/etc/mdadm.conf which did very well. Especially since drive
letters danced around quite a bit between reboots. One of the
disks died during transit, and the redundancy part of RAID
earned its keep. The only thing I didn't figure out was SATA
hotplug. The SATA controller (an Areca 1230 in JBOD mode)
happily noticed when a drive was hotplugged into a port. But
Linux didn't seem to notice. I was using cfdisk to probe.
Is there a particular command needed to convince Linux to
look around and see if there are any new SATA devices?

Jeff