Re: mbr-install for Raid 1

Re: mbr-install for Raid 1

[Michael Tokarev]

[I'm getting quite some questions similar to this
  one -- so instead of replying to every and each,
  I'm posting to linux-raid@, to be able to refer to
  this post in the future... ;)]

Zeno R.R. Davatz wrote:
> Hi!
> 
> I am just reading a post of yours regarding using 'install-mbr' for linux-raid.
> 
> Something I do not understand about the post:
> http://lists.debian.org/debian-testing/2004/04/msg00054.html
> 
> is following:
> "mark your boot raid partitions active...". What do you mean by that?

Set the partitions (single partition on every disk) where your root raid
device resides to be active with fdisk.

> Do you mean to mark all the first partitions of all the disks /dev/sd[abcd]1 as boot with fdisk?

Not necessary first ones, but it is simpler to have your root fs on
first partition.  Again, it is the root-raid partition that should
be active.

> In that case I would have to do install-mbr /dev/md0 --force

No, you would have to use boot=/dev/md0 in your lilo.conf,
and install-mbr /dev/sd[abcd]1.

> Is that correct?

Basically, the scenario is as follows.

Standard mbr (master boot record) from mbr package (note lilo also
have it, see lilo -M) is installed into standard place (where BIOS
will expect it to be) into all your disks once (don't forget to
install the same mbr when you plug new disk).  The mbr code (it
resides on the first sector of the disk) works by reading partition
table, finding partition marked as "active" (or "boot" -- the same
flag but different terminology), loading boot record from that
partition and executing it.  Mbr code is stable and you don't have
to change it -- the first sector of your disks will never change.
In contrast, you will do eg kernel upgrades and similar stuff,
for which lilo boot tables needs to be refreshed, and that should
be done on all disks (to be able to boot off any disk in case
first one fails).  For this to work, you set up lilo to write
it's boot record into the device where your root filesystem is --
it is raid1 array created off all active (boot) partitions of
all your disks.  Lilo writes boot record into the beginning of
md0, and raid code propagates that boot record into your disks,
all of them -- remember, md0 is composed of active partitions
on all your disks -- this is exactly the place where mbr code
will look for the bootloader.

So, you have the same mbr code on all your disks (installed
once when you configure each disk), and "second-stage" boot
record, installed by lilo into md0 and again propagated to
all disks (into active or boot partition of each), which will
be loaded by mbr -- this boot record will be updated -- on
all disks -- when you re-run lilo.  In case any disk fails,
you have the same boot code and sequence on every other disk,
so you could boot off any working, non-failed disk.

But be warned -- boot (active) partition on every disk should
be at the exactly same place, or else file offsets written by
lilo will be valid for one disk but not valid for other.

/mjt

Re: mbr-install for Raid 1

[Zeno R.R. Davatz]

Hi!

Thanks for your prompt and detailed response, I appreciate your time! I will post it on our website as well.

I done as follows and get the following:

On Tue, 05 Oct 2004 13:08:19 +0400
Michael Tokarev <mjt@tls.msk.ru> wrote:
> No, you would have to use boot=/dev/md0 in your lilo.conf,
> and install-mbr /dev/sd[abcd]1.

Now when I boot, I get

MBR FA: 

I hit A for 'Advanced', then I get:

MBR 1234A:

Then I hit '1' then I get:

MBR
MBR
MBR FA:

And nothing happens :-(

Any hints?

Thanks for your Feedback.

Zeno

Re: mbr-install for Raid 1

[Zeno R.R. Davatz]

Hi

I am just thinking of one more problem that turned up.

You suppose that I am running a RAID1 as you say I should install the boot-image of lilo to my root partition because Install-Mbr checks for it there. My problem: My Root-Partition is a RAID5. I would like to boot from a RAID1 and get my RAID5 going from there.

Any hints?
Zeno

On Tue, 05 Oct 2004 13:08:19 +0400
Michael Tokarev <mjt@tls.msk.ru> wrote:

> [I'm getting quite some questions similar to this
>   one -- so instead of replying to every and each,
>   I'm posting to linux-raid@, to be able to refer to
>   this post in the future... ;)]
> 
> Zeno R.R. Davatz wrote:
> > Hi!
> > 
> > I am just reading a post of yours regarding using 'install-mbr' for linux-raid.
> > 
> > Something I do not understand about the post:
> > http://lists.debian.org/debian-testing/2004/04/msg00054.html
> > 
> > is following:
> > "mark your boot raid partitions active...". What do you mean by that?
> 
> Set the partitions (single partition on every disk) where your root raid
> device resides to be active with fdisk.
> 
> > Do you mean to mark all the first partitions of all the disks /dev/sd[abcd]1 as boot with fdisk?
> 
> Not necessary first ones, but it is simpler to have your root fs on
> first partition.  Again, it is the root-raid partition that should
> be active.
> 
> > In that case I would have to do install-mbr /dev/md0 --force
> 
> No, you would have to use boot=/dev/md0 in your lilo.conf,
> and install-mbr /dev/sd[abcd]1.
> 
> > Is that correct?
> 
> Basically, the scenario is as follows.
> 
> Standard mbr (master boot record) from mbr package (note lilo also
> have it, see lilo -M) is installed into standard place (where BIOS
> will expect it to be) into all your disks once (don't forget to
> install the same mbr when you plug new disk).  The mbr code (it
> resides on the first sector of the disk) works by reading partition
> table, finding partition marked as "active" (or "boot" -- the same
> flag but different terminology), loading boot record from that
> partition and executing it.  Mbr code is stable and you don't have
> to change it -- the first sector of your disks will never change.
> In contrast, you will do eg kernel upgrades and similar stuff,
> for which lilo boot tables needs to be refreshed, and that should
> be done on all disks (to be able to boot off any disk in case
> first one fails).  For this to work, you set up lilo to write
> it's boot record into the device where your root filesystem is --
> it is raid1 array created off all active (boot) partitions of
> all your disks.  Lilo writes boot record into the beginning of
> md0, and raid code propagates that boot record into your disks,
> all of them -- remember, md0 is composed of active partitions
> on all your disks -- this is exactly the place where mbr code
> will look for the bootloader.
> 
> So, you have the same mbr code on all your disks (installed
> once when you configure each disk), and "second-stage" boot
> record, installed by lilo into md0 and again propagated to
> all disks (into active or boot partition of each), which will
> be loaded by mbr -- this boot record will be updated -- on
> all disks -- when you re-run lilo.  In case any disk fails,
> you have the same boot code and sequence on every other disk,
> so you could boot off any working, non-failed disk.
> 
> But be warned -- boot (active) partition on every disk should
> be at the exactly same place, or else file offsets written by
> lilo will be valid for one disk but not valid for other.
> 
> /mjt
> 


-- 
Mit freundlichen Grüssen / best regards

Zeno Davatz
Verkauf & Akquisition

+41 1 350 85 86

www.ywesee.com > intellectual capital connected > www.oddb.org
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Re: mbr-install for Raid 1

[Bernd Fischer]

Zeno R.R. Davatz wrote:

 > I am just thinking of one more problem that turned up.

 > You suppose that I am running a RAID1 as you say I should install the
 > boot-image of lilo to my root partition because Install-Mbr checks
 > for it there. My problem: My Root-Partition is a RAID5. I would like
 > to boot from a RAID1 and get my RAID5 going from there.

Basically the same procedure. Just replace the words "root partition"
with "boot partition" or "partition on which you install your kernel" in
Michaels instructions.

Bernd Fischer

Re: mbr-install for Raid 1 with Root on Raid5

[Zeno R.R. Davatz]

Bernd!

thanks for your Mail, Time and Help.

On Tue, 05 Oct 2004 20:25:02 +0200
Bernd Fischer wrote:
>  > You suppose that I am running a RAID1 as you say I should install the
>  > boot-image of lilo to my root partition because Install-Mbr checks
>  > for it there. My problem: My Root-Partition is a RAID5. I would like
>  > to boot from a RAID1 and get my RAID5 going from there.
> 
> Basically the same procedure. Just replace the words "root partition"
> with "boot partition" or "partition on which you install your kernel" in
> Michaels instructions.
I'm doing exactly that or at least I believe so.

I run 
install-mbr -t 150 /dev/sda1
install-mbr -t 150 /dev/sdb1
install-mbr -t 150 /dev/sdc1
install-mbr -t 150 /dev/sdd1

then in lilo.conf I put 

boot = /dev/md0
root = /dev/md2

then I reboot and I get:

MBR FA: (I hit 'A')
MBR 1234F: (I hit '1')
MBR
MBR FA: 

.. and nothing boots. MBR just stands there forever.

Any hints?

Thanks for your Feedback.

Zeno

PS: Lilo can not write it's boot-image on RAID5, only on RAID1.

Re: mbr-install for Raid 1, rerun Lilo necessary?

[Zeno R.R. Davatz]

On Tue, 05 Oct 2004 13:08:19 +0400
Michael Tokarev <mjt@tls.msk.ru> wrote:

> No, you would have to use boot=/dev/md0 in your lilo.conf,
Do I have to run 'lilo -v' so lilo gets this?

Because whenever I run lilo -v (22.5.8) with 'boot=/dev/md0 I get the wonderful Error of:
Fatal: Trying to map files from unnamed device 0x0000 (NFS ?)

Any hints?

Thanks
Zeno

Re: mbr-install for Raid 1, rerun Lilo necessary?

[Bernd Fischer]

Zeno R.R. Davatz wrote:

>> No, you would have to use boot=/dev/md0 in your lilo.conf,

> Do I have to run 'lilo -v' so lilo gets this?

As usual, you have to run lilo everytime you install a new kernel or 
edit lilo.conf

> Because whenever I run lilo -v (22.5.8) with 'boot=/dev/md0 I get the wonderful Error of:
> Fatal: Trying to map files from unnamed device 0x0000 (NFS ?)

> Any hints?

I had the same problem some time ago. AFAIR it went away when I updated 
to lilo 22.6
As a workaround, create a symlink to /dev/md0 ( e.g. /dev/MD0 ) and use 
this as your boot device in lilo.conf.

Bernd Fischer

Re: mbr-install for Raid 1, mdadm -a /dev/md0 /dev/sda1

[Zeno R.R. Davatz]

Hi Bernd

Thanks for your prompt reply.

On Wed, 06 Oct 2004 18:16:57 +0200
Bernd Fischer wrote:

> Zeno R.R. Davatz wrote:
> 
> >> No, you would have to use boot=/dev/md0 in your lilo.conf,
> 
> > Do I have to run 'lilo -v' so lilo gets this?
> 
> As usual, you have to run lilo everytime you install a new kernel or 
> edit lilo.conf
> 
> > Because whenever I run lilo -v (22.5.8) with 'boot=/dev/md0 I get the wonderful Error of:
> > Fatal: Trying to map files from unnamed device 0x0000 (NFS ?)
> 
> > Any hints?
> 
> I had the same problem some time ago. AFAIR it went away when I updated 
> to lilo 22.6
> As a workaround, create a symlink to /dev/md0 ( e.g. /dev/MD0 ) and use 
> this as your boot device in lilo.conf.
I managed to boot my /dev/md2 (using find . -xdev | cpio -pm /mnt/newroot instead of cp -ax / /mnt/newroot to copy my system to Raid). Now I am doing 'mdadam -a /dev/md2 /dev/sda3'

as next I would do 'mdadm -a /dev/md0 /dev/sda1'

Will the lilo problem then vanish?

Thanks for your Feedback.
Zeno