Adding a mirror to a RAID1 Device

Adding a mirror to a RAID1 Device

[Caleb Crome]

Hello all, I've got a peculiar problem.  I added some new disk space to my
system (Linux 2.4.19, Mandrake), and created a RAID1 drive /dev/md0 with
only 1 active mirror because I didn't have enough space (yet) to put
everything on my new raid drive.  I had the intention of then addeding
another disk to the raid setup later so that it would just
auto-reconsctruct and be ready to go.

However, when I do raidhotadd, I doesn't seem to reconsctruct.


So, my /proc/mdstat looks like this:

Personalities : [raid1]
read_ahead 1024 sectors
md0 : active raid1 ide/host0/bus1/target0/lun0/part3[0]
      81920064 blocks [1/1] [U]


When I
   raidhotadd /dev/md0  /dev/ide/host0/bus0/target0/lun0/part3

I get the following /proc/mdstat:

Personalities : [raid1]
read_ahead 1024 sectors
md0 : active raid1 ide/host0/bus1/target0/lun0/part3[0] \ <contd.>
                   ide/host0/bus0/target0/lun0/part3[0]
      81920064 blocks [1/1] [U]

unused devices: <none>


It doesn't reconsctruct the drive from bus0 as I expected it to.  What do
I do to convince the kernel to do the reconstruction?

Thanks,
-Caleb

Re: Adding a mirror to a RAID1 Device

[Neil Brown]

On Monday November 24, linux-raid@crome.org wrote:
> Hello all, I've got a peculiar problem.  I added some new disk space to my
> system (Linux 2.4.19, Mandrake), and created a RAID1 drive /dev/md0 with
> only 1 active mirror because I didn't have enough space (yet) to put
> everything on my new raid drive.  I had the intention of then addeding
> another disk to the raid setup later so that it would just
> auto-reconsctruct and be ready to go.

Sorry, but that was the wrong thing to do.
A raid1 with only one drive is pretty pointless, but you asked for it
and you got it :-)

What you should have done is make a raid1 with 2 drives, one of which
was missing/failed.  With mdadm, the command would be:

  mdadm -C /dev/md0 --level=raid1 --disks=2 /dev/hda3 missing

then you can hot-add the extra drive when it arrives.

What you have to do now is recreate the raid1 with two drives.  You
will have to have the filesystem unmounted and the raid stopped, but
you will not lose any data.

NeilBrown

Re: Adding a mirror to a RAID1 Device

[jlewis]

On Tue, 25 Nov 2003, Neil Brown wrote:

> What you should have done is make a raid1 with 2 drives, one of which
> was missing/failed.  With mdadm, the command would be:
> 
>   mdadm -C /dev/md0 --level=raid1 --disks=2 /dev/hda3 missing
> 
> then you can hot-add the extra drive when it arrives.
> 
> What you have to do now is recreate the raid1 with two drives.  You
> will have to have the filesystem unmounted and the raid stopped, but
> you will not lose any data.

I have a somewhat related question.  Suppose I have a system with RAID1 
(several md devices) using identical partitions on hda and hdc.  When a 
card that works arrives, I want to move these two disks to the faster ATA 
interfaces, which will likely make then hde and hdg.  

To do this, can I fail hdc, move it to hde, edit the raidtab on hde to say
that the md devices are hde and hdg, start up that "new" RAID1 degraded,
then pull hda, and hot add it to the new md devices and resync?

Is there a better way to get these 2 disks moved from the ATA33 
motherboard interfaces to an ATA100 controller card?  Perhaps just boot in 
rescue mode from a CD (system told me a bootfloppy could not be made due 
to kernel/modules sizes) edit raidtab and then just reboot?
 
----------------------------------------------------------------------
 Jon Lewis *jlewis@lewis.org*|  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |  
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________

Re: Adding a mirror to a RAID1 Device

[Neil Brown]

On Tuesday November 25, jlewis@lewis.org wrote:
> On Tue, 25 Nov 2003, Neil Brown wrote:
> 
> > What you should have done is make a raid1 with 2 drives, one of which
> > was missing/failed.  With mdadm, the command would be:
> > 
> >   mdadm -C /dev/md0 --level=raid1 --disks=2 /dev/hda3 missing
> > 
> > then you can hot-add the extra drive when it arrives.
> > 
> > What you have to do now is recreate the raid1 with two drives.  You
> > will have to have the filesystem unmounted and the raid stopped, but
> > you will not lose any data.
> 
> I have a somewhat related question.  Suppose I have a system with RAID1 
> (several md devices) using identical partitions on hda and hdc.  When a 
> card that works arrives, I want to move these two disks to the faster ATA 
> interfaces, which will likely make then hde and hdg.  
> 
> To do this, can I fail hdc, move it to hde, edit the raidtab on hde to say
> that the md devices are hde and hdg, start up that "new" RAID1 degraded,
> then pull hda, and hot add it to the new md devices and resync?
> 
> Is there a better way to get these 2 disks moved from the ATA33 
> motherboard interfaces to an ATA100 controller card?  Perhaps just boot in 
> rescue mode from a CD (system told me a bootfloppy could not be made due 
> to kernel/modules sizes) edit raidtab and then just reboot?

Just 
   power down the machine
   move the drives
   power up again

all is done.... unless you are using raidstart, but that is
universally a mistake.

If you are using "Linux RAID" partition types, the kernel will find
the partitions in their new location and assemble them for you just as
it is now.
If you are using mdadm to assemble you arrays (which I suspect you
aren't as you talk about 'raidtab') then it will find them just as
easily in the new location, providing you have include the new devices
in the "DEVICES" line of mdadm.conf.

If you are using raidstart to start your arrays, then stop doing that
straight away and us a reliable method.

You do not need to edit raidtab to reflect any changes you make.
raidtab is primarily use for *creating* raid arrays, not for managaing
them.

NeilBrown

Re: Adding a mirror to a RAID1 Device

[Dan Egli]

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Neil Brown wrote:

|
| all is done.... unless you are using raidstart, but that is
| universally a mistake.

But all linux distributions I've used, save perhaps gentoo, DO use
raidstart with /etc/raidtab. How do you configure it so the kernel
assembles the array for you? /etc/fstab?

- --- Dan

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Re: Adding a mirror to a RAID1 Device

[Luca Berra]

On Tue, Nov 25, 2003 at 03:06:50PM -0700, Dan Egli wrote:
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>Neil Brown wrote:
>
>|
>| all is done.... unless you are using raidstart, but that is
>| universally a mistake.
>
>But all linux distributions I've used, save perhaps gentoo, DO use
>raidstart with /etc/raidtab. How do you configure it so the kernel
>assembles the array for you? /etc/fstab?
>
for mandrake linux you can use my packages:
http://www.comedia.it/~bluca/cooker/lvm2/
(you only need initscripts, you might need the mdadm there and mkinitrd,
if you have root raid)

L.

-- 
Luca Berra -- bluca@comedia.it
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Re: Adding a mirror to a RAID1 Device

[Dan Egli]

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Luca Berra wrote:

| On Tue, Nov 25, 2003 at 03:06:50PM -0700, Dan Egli wrote:
|
|> -----BEGIN PGP SIGNED MESSAGE-----
|> Hash: SHA1
|>
|> Neil Brown wrote:
|>
|> |
|> | all is done.... unless you are using raidstart, but that is
|> | universally a mistake.
|>
|> But all linux distributions I've used, save perhaps gentoo, DO use
|> raidstart with /etc/raidtab. How do you configure it so the kernel
|> assembles the array for you? /etc/fstab?
|>
| for mandrake linux you can use my packages:
| http://www.comedia.it/~bluca/cooker/lvm2/
| (you only need initscripts, you might need the mdadm there and mkinitrd,
| if you have root raid)

Sorry, but I do not now, nor will I ever use Mandrake. I despise any
linux distribution that tries as hard as Mandrake does to isolate the
user from the config files. As far as I'm conserned, Mandrake is not
even a real linux distribution.

There's two Distributions I'd be interested in hearing about:
RedHat/Fedora
Gentoo

If you know how to accomplish that with either of these, I'm all ears.

- --- Dan
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Re: Adding a mirror to a RAID1 Device

[jlewis]

On Tue, 25 Nov 2003, Dan Egli wrote:

> | all is done.... unless you are using raidstart, but that is
> | universally a mistake.
> 
> But all linux distributions I've used, save perhaps gentoo, DO use
> raidstart with /etc/raidtab. How do you configure it so the kernel
> assembles the array for you? /etc/fstab?

I'll have to add some debug echos to be sure, but it looks like Fedora 
Core 1 uses raidstart (from /etc/rc.d/rc.sysinit) only if the kernel 
didn't auto-start the devices.

----------------------------------------------------------------------
 Jon Lewis *jlewis@lewis.org*|  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |  
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________

Re: Adding a mirror to a RAID1 Device

[Luca Berra]

On Tue, Nov 25, 2003 at 03:56:25PM -0700, Dan Egli wrote:
>Sorry, but I do not now, nor will I ever use Mandrake. I despise any
>linux distribution that tries as hard as Mandrake does to isolate the
>user from the config files. As far as I'm conserned, Mandrake is not
>even a real linux distribution.
I am not sure we are talking about the same distribution. But i do not
care to start a distro war here nor anywhere else.

>There's two Distributions I'd be interested in hearing about:
>RedHat/Fedora
Mandrake initscripts/mkinitrd are derived from Redhat's, so it should be possible
to merge changes in Fedora
>Gentoo
never used Gentoo, so i don't have the faintest idea of what they have
in place.

L.

-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
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Re: Adding a mirror to a RAID1 Device

[jlewis]

On Wed, 26 Nov 2003, Neil Brown wrote:

> Just 
>    power down the machine
>    move the drives
>    power up again
> 
> all is done.... unless you are using raidstart, but that is
> universally a mistake.

That was amazing.  My Promise (Ultra100TX2) card arrived today.  I did a 
shutdown, put the card in, moved hda and hdc onto it, powered up, and it 
booted right up.  The kernel did notice that the md device members' device 
names had changed, but it found them and "just worked".  

Again, this was Red Hat's Fedora Core 1, with all partitions being RAID1 
and a pair of WD ATA100 160gb drives.

----------------------------------------------------------------------
 Jon Lewis *jlewis@lewis.org*|  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |  
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________

Re: Adding a mirror to a RAID1 Device

[H. Peter Anvin]

Followup to:  <16323.732.390200.935640@notabene.cse.unsw.edu.au>
By author:    Neil Brown <neilb@cse.unsw.edu.au>
In newsgroup: linux.dev.raid
> 
> What you should have done is make a raid1 with 2 drives, one of which
> was missing/failed.  With mdadm, the command would be:
> 
>   mdadm -C /dev/md0 --level=raid1 --disks=2 /dev/hda3 missing
> 
> then you can hot-add the extra drive when it arrives.
> 
> What you have to do now is recreate the raid1 with two drives.  You
> will have to have the filesystem unmounted and the raid stopped, but
> you will not lose any data.
> 

For the case of RAID-1 in particular, it would be nice to be able to
hotadd drives "ad infinitum"... after all they're all the same.

	-hpa
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