non fs-data and gpt partitioned md

non fs-data and gpt partitioned md

[Ken Gunderson]

Hello:

I'm wanting to set up a new md root lvm based configuration and after
reading various docs am confused about how I should be going about this.
My intent is to have mirrored /boot and swap partitions and a raid10 /
partition with LVM.

Issue #1: gpt is recommended over mbr based partitioning for new
installs, even on BIOS based systems (presuming these BIOS will boot
gpt, wh/mine do). Auto-assemble is not recommended for new installations
(my understanding is that it is not necessary with initramfs) so I
presume I should be specifying partition type DA.  However, while gdisk
et.al. allow for selecting type FD, they do not offer DA as an option.  

Issue #2: Is there any reason to prefer 1.0 vs. 1.2 metadata? I can use
either grub2 or Syslinux boot loaders.  My understanding is that
Syslinux supports the former while Grub2 supports 1.2. All other things
being equal, I'd prefer to use Syslinux.  Unless there is some technical
reason to favor 1.2 metadata and/or Grub2.

So what would be best practices recommended way to proceed here?

Thanks-- Ken

-- 
Ken Gunderson <kgunders@teamcool.net>

Re: non fs-data and gpt partitioned md

[Ken Gunderson]

On Tue, 17 Apr 2012 14:40:10 -0600
Ken Gunderson <kgunders@teamcool.net> wrote:

Apologies for following my own post but I guess should elaborate...

> Hello:
> 
> I'm wanting to set up a new md root lvm based configuration and after
> reading various docs am confused about how I should be going about
> this. My intent is to have mirrored /boot and swap partitions and a
> raid10 / partition with LVM.
> 
> Issue #1: gpt is recommended over mbr based partitioning for new
> installs, even on BIOS based systems (presuming these BIOS will boot
> gpt, wh/mine do). Auto-assemble is not recommended for new
> installations (my understanding is that it is not necessary with
> initramfs) so I presume I should be specifying partition type DA.
> However, while gdisk et.al. allow for selecting type FD, they do not
> offer DA as an option.

Per <http://www.rodsbooks.com/linux-fs-code.html>, Linux ignores
partition type codes.  Yet per man mdadm:

"When creating a partition based array,  using  mdadm  with
version-1.x metadata, the partition type should be set to 0xDA (non
fs-data).  This type selection allows for greater precision since using
any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
might create prob‐ lems in the event of array recovery through a live
cdrom."

So which is it?  Does partition type code matter to md/mdadm or not?
 
> Issue #2: Is there any reason to prefer 1.0 vs. 1.2 metadata? I can
> use either grub2 or Syslinux boot loaders.  My understanding is that
> Syslinux supports the former while Grub2 supports 1.2. All other
> things being equal, I'd prefer to use Syslinux.  Unless there is some
> technical reason to favor 1.2 metadata and/or Grub2.
> 
> So what would be best practices recommended way to proceed here?

The reason I ask is that I bring such a configuration online on
Archlinux by following these instructions:

<https://wiki.archlinux.org/index.php/Software_RAID_and_LVM>

But I'll be damned if I can recover from failed drive simulations - at
least reliably, as sometimes it works while others not - so I'm just
trying to rule out potential variables here.

Thanks-- Ken

-- 
Ken Gunderson <kgunders@teamcool.net>
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Re: non fs-data and gpt partitioned md

[NeilBrown]

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On Wed, 18 Apr 2012 18:18:33 -0600 Ken Gunderson <kgunders@teamcool.net>
wrote:

> On Tue, 17 Apr 2012 14:40:10 -0600
> Ken Gunderson <kgunders@teamcool.net> wrote:
> 
> Apologies for following my own post but I guess should elaborate...
> 
> > Hello:
> > 
> > I'm wanting to set up a new md root lvm based configuration and after
> > reading various docs am confused about how I should be going about
> > this. My intent is to have mirrored /boot and swap partitions and a
> > raid10 / partition with LVM.
> > 
> > Issue #1: gpt is recommended over mbr based partitioning for new
> > installs, even on BIOS based systems (presuming these BIOS will boot
> > gpt, wh/mine do). Auto-assemble is not recommended for new
> > installations (my understanding is that it is not necessary with
> > initramfs) so I presume I should be specifying partition type DA.
> > However, while gdisk et.al. allow for selecting type FD, they do not
> > offer DA as an option.
> 
> Per <http://www.rodsbooks.com/linux-fs-code.html>, Linux ignores
> partition type codes.  Yet per man mdadm:
> 
> "When creating a partition based array,  using  mdadm  with
> version-1.x metadata, the partition type should be set to 0xDA (non
> fs-data).  This type selection allows for greater precision since using
> any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
> might create prob‐ lems in the event of array recovery through a live
> cdrom."
> 
> So which is it?  Does partition type code matter to md/mdadm or not?

Both.  Neither. 

md does handle 0xFD partitions a bit differently, but I recommend not using
that feature.
Other than that md igores them.  mdadm ingores them completely.

But other tools - typically installers - might pay some attention to them.
Using 0xDA discourages such tools from mishandling them.

>  
> > Issue #2: Is there any reason to prefer 1.0 vs. 1.2 metadata? I can
> > use either grub2 or Syslinux boot loaders.  My understanding is that
> > Syslinux supports the former while Grub2 supports 1.2. All other
> > things being equal, I'd prefer to use Syslinux.  Unless there is some
> > technical reason to favor 1.2 metadata and/or Grub2.
> > 
> > So what would be best practices recommended way to proceed here?
> 
> The reason I ask is that I bring such a configuration online on
> Archlinux by following these instructions:
> 
> <https://wiki.archlinux.org/index.php/Software_RAID_and_LVM>
> 
> But I'll be damned if I can recover from failed drive simulations - at
> least reliably, as sometimes it works while others not - so I'm just
> trying to rule out potential variables here.
> 
> Thanks-- Ken
> 

Any reason for preferring one of 1.0 and 1.2 is out side of md.

Maybe you want to be able to mount one half of a RAID1 independently.  You
need 1.0 for that.  Maybe you want to ensure that never happens.  Then 1.2 is
better. Maybe your boot loaded only works with one.  Then the choice is clear.

NeilBrown


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Re: non fs-data and gpt partitioned md

[Ken Gunderson]

On Thu, 19 Apr 2012 10:38:23 +1000
NeilBrown <neilb@suse.de> wrote:

> On Wed, 18 Apr 2012 18:18:33 -0600 Ken Gunderson
> <kgunders@teamcool.net> wrote:
> 
> > On Tue, 17 Apr 2012 14:40:10 -0600
> > Ken Gunderson <kgunders@teamcool.net> wrote:
> > 
> > Apologies for following my own post but I guess should elaborate...
> > 
> > > Hello:
> > > 
> > > I'm wanting to set up a new md root lvm based configuration and
> > > after reading various docs am confused about how I should be
> > > going about this. My intent is to have mirrored /boot and swap
> > > partitions and a raid10 / partition with LVM.
> > > 
> > > Issue #1: gpt is recommended over mbr based partitioning for new
> > > installs, even on BIOS based systems (presuming these BIOS will
> > > boot gpt, wh/mine do). Auto-assemble is not recommended for new
> > > installations (my understanding is that it is not necessary with
> > > initramfs) so I presume I should be specifying partition type DA.
> > > However, while gdisk et.al. allow for selecting type FD, they do
> > > not offer DA as an option.
> > 
> > Per <http://www.rodsbooks.com/linux-fs-code.html>, Linux ignores
> > partition type codes.  Yet per man mdadm:
> > 
> > "When creating a partition based array,  using  mdadm  with
> > version-1.x metadata, the partition type should be set to 0xDA (non
> > fs-data).  This type selection allows for greater precision since
> > using any other [RAID auto-detect (0xFD) or a GNU/Linux partition
> > (0x83)], might create prob‐ lems in the event of array recovery
> > through a live cdrom."
> > 
> > So which is it?  Does partition type code matter to md/mdadm or not?
> 
> Both.  Neither. 
> 
> md does handle 0xFD partitions a bit differently, but I recommend not
> using that feature.
> Other than that md igores them.  mdadm ingores them completely.
> 
> But other tools - typically installers - might pay some attention to
> them. Using 0xDA discourages such tools from mishandling them.

Thanks for the clarification.  
 
> > > Issue #2: Is there any reason to prefer 1.0 vs. 1.2 metadata? I
> > > can use either grub2 or Syslinux boot loaders.  My understanding
> > > is that Syslinux supports the former while Grub2 supports 1.2.
> > > All other things being equal, I'd prefer to use Syslinux.  Unless
> > > there is some technical reason to favor 1.2 metadata and/or Grub2.
> > > 
> > > So what would be best practices recommended way to proceed here?
> > 
> > The reason I ask is that I bring such a configuration online on
> > Archlinux by following these instructions:
> > 
> > <https://wiki.archlinux.org/index.php/Software_RAID_and_LVM>
> > 
> > But I'll be damned if I can recover from failed drive simulations -
> > at least reliably, as sometimes it works while others not - so I'm
> > just trying to rule out potential variables here.
> > 
> > Thanks-- Ken
> > 
> 
> Any reason for preferring one of 1.0 and 1.2 is out side of md.
> 
> Maybe you want to be able to mount one half of a RAID1
> independently.  You need 1.0 for that.  Maybe you want to ensure that
> never happens.  Then 1.2 is better. Maybe your boot loaded only works
> with one.  Then the choice is clear.

Well, this only pertains to /boot partition, so there's nothing to stop
one from mixing and matching, e.g. Syslinux using 1.0 metadata for
RAID1 /boot and 1.2 metadata for RAID10 swap and root devices, no? Or
is this not advisable?

Thanks-- Ken

-- 
Ken Gunderson <kgunders@teamcool.net>
--
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Re: non fs-data and gpt partitioned md

[NeilBrown]

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On Wed, 18 Apr 2012 19:02:21 -0600 Ken Gunderson <kgunders@teamcool.net>
wrote:


> > Any reason for preferring one of 1.0 and 1.2 is out side of md.
> > 
> > Maybe you want to be able to mount one half of a RAID1
> > independently.  You need 1.0 for that.  Maybe you want to ensure that
> > never happens.  Then 1.2 is better. Maybe your boot loaded only works
> > with one.  Then the choice is clear.
> 
> Well, this only pertains to /boot partition, so there's nothing to stop
> one from mixing and matching, e.g. Syslinux using 1.0 metadata for
> RAID1 /boot and 1.2 metadata for RAID10 swap and root devices, no? Or
> is this not advisable?

That is all fine.

NeilBrown

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