d-i: partitioned md devices? allowed but not supported?

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d-i: partitioned md devices? allowed but not supported?

Bernd Eckenfels-2
Hello,

I just used net-install to install on a md raid device. The debian installer
is happyly allowing me to place a single primary msdos partition on both of
my disks. make the partition of type md raid, and add those with the md
configurator into a single raid1 raid.

If i then place a partition on the resulting device (md0) I can add
partitions for /, /usr, swap, etc. The installer partition wizard will
create /dev/md0pX devices.

However the problem is, that the installer system does not know those
dynamic partitioned device files (mdp dynamic major).

IMHO we should disable paritioning md devices or at least print out a
warning, that mdadm needs to create the device files.

Also: the naming conventions are different in some documentation and source,
one does also find md_pX and I think the linux kernel does even register
md0/dX?

BTW: does anybody know how to auto-start more than one (the first?) raid
error by the kernel?

Greetings
Bernd
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Re: d-i: partitioned md devices? allowed but not supported?

Henrique de Moraes Holschuh
On Thu, 03 Nov 2005, Bernd Eckenfels wrote:
> If i then place a partition on the resulting device (md0) I can add
> partitions for /, /usr, swap, etc. The installer partition wizard will
> create /dev/md0pX devices.

These are not well supported by anything.  Lilo will croak. grub is grub is
grub, and will eat grub instead of working.  The kernel people sounded not
very commited to partitioned md devices last time I looked after it (because
I **HATE** more than one md device per disk, as the md driver is stupid
enough to not know about other md devices in the same disk and does stupid
things).

I suggest you go with lvm2 (or other device-manager based system) on top of
a simple md array.  It is much safer in the long run, even if it means
initrds (yuck).

> IMHO we should disable paritioning md devices or at least print out a
> warning, that mdadm needs to create the device files.

Agreed.

> BTW: does anybody know how to auto-start more than one (the first?) raid
> error by the kernel?

"error"?

I always auto-start at least three md devices, it works just like one
expects it to.  But don't expect *NESTED* md devices to autostart.  In fact,
don't nest md devices, it ain't safe, it is one of those places where the
bugs have never been really shaken out of the system.

--
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh


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Re: d-i: partitioned md devices? allowed but not supported?

Roberto C. Sanchez
On Thu, Nov 03, 2005 at 11:17:41PM -0200, Henrique de Moraes Holschuh wrote:

> On Thu, 03 Nov 2005, Bernd Eckenfels wrote:
> > If i then place a partition on the resulting device (md0) I can add
> > partitions for /, /usr, swap, etc. The installer partition wizard will
> > create /dev/md0pX devices.
>
> These are not well supported by anything.  Lilo will croak. grub is grub is
> grub, and will eat grub instead of working.  The kernel people sounded not
> very commited to partitioned md devices last time I looked after it (because
> I **HATE** more than one md device per disk, as the md driver is stupid
> enough to not know about other md devices in the same disk and does stupid
> things).
>
> I suggest you go with lvm2 (or other device-manager based system) on top of
> a simple md array.  It is much safer in the long run, even if it means
> initrds (yuck).
>
As long as you place / (and /boot, if seperate) on a small non-LVM
partition (it can even be RAID1), then you are fine to boot without an
initrd.

> > IMHO we should disable paritioning md devices or at least print out a
> > warning, that mdadm needs to create the device files.
>
> Agreed.
>
> > BTW: does anybody know how to auto-start more than one (the first?) raid
> > error by the kernel?
>
> "error"?
>
> I always auto-start at least three md devices, it works just like one
> expects it to.  But don't expect *NESTED* md devices to autostart.  In fact,
> don't nest md devices, it ain't safe, it is one of those places where the
> bugs have never been really shaken out of the system.
>
Agreed.  Last night I was installing on some old hardware and I had a
hard drive go bad after the first reboot.  The drive was on /dev/md1.
All three arrays (md0, md1, and md2) came up, with only md1 in a
degraded state.

-Roberto

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Roberto C. Sanchez
http://familiasanchez.net/~roberto

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Re: d-i: partitioned md devices? allowed but not supported?

Bernd Eckenfels
In reply to this post by Henrique de Moraes Holschuh
In article <[hidden email]> you wrote:
> I suggest you go with lvm2 (or other device-manager based system) on top of
> a simple md array.  It is much safer in the long run, even if it means
> initrds (yuck).

I did this. But actually I have 2 partitions, one containing md0 with ext3
root and the other containing md1 with a physical volume.

>> BTW: does anybody know how to auto-start more than one (the first?) raid
>> error by the kernel?
>
> "error"?

skip the "error" word :)

> I always auto-start at least three md devices, it works just like one

Well, with auto start i mean the fact that the kernel finds the devices and
starts them. I suspect it is doing that because there is a bootflag on the
partition. I am not sure if the kernel can du that for all devices it auto
detected (i havd md0 on sda1/sdb1 and md1 on sda2/sdb2, only the first is
available before init).

Gruss
Bernd


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Re: d-i: partitioned md devices? allowed but not supported?

Henrique de Moraes Holschuh
On Fri, 04 Nov 2005, Bernd Eckenfels wrote:
> starts them. I suspect it is doing that because there is a bootflag on the
> partition. I am not sure if the kernel can du that for all devices it auto

It looks for all type 0xFD partitions.

> detected (i havd md0 on sda1/sdb1 and md1 on sda2/sdb2, only the first is
> available before init).

It will autorun/enable *all* md devices it can, not just md0.  All of them
will be available to bootstrap, and telling the kernel (through the command
line) to mount a root partition in /dev/md1 will work just fine). This was
true the last time I tried that, anyway, which was about one year ago.

--
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh


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Re: d-i: partitioned md devices? allowed but not supported?

Bernd Eckenfels
In article <[hidden email]> you wrote:
> It will autorun/enable *all* md devices it can, not just md0.  All of them
> will be available to bootstrap, and telling the kernel (through the command
> line) to mount a root partition in /dev/md1 will work just fine). This was
> true the last time I tried that, anyway, which was about one year ago.

Yes I guessed so, however it does not do it. In dmesg I only see md0
discovered, md1 does work only after putting it in mdadm.conf and using
mdrun

Well, I cant investigate on the system in question since it is now
productive, but will check another one. Thanks for your reply.

Gruss
Bernd


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