mdadm 1.x device naming

mdadm 1.x device naming

[Colin Watson]

I've been looking at Felix's raid branch which adds support for mdadm
metadata version 1.x, and trying to bring it up to date.  The first
thing I noticed was an issue with device naming.  With mdadm metadata
0.9, md devices were just numbered.  Easy.  With mdadm metadata 1.x,
devices can also be named, which gives you things like /dev/md/home.
(There's also a "homehost" quirk for arrays that can be attached to
multiple hosts; I propose to ignore this for now.)

In many ways this is better.  Named devices means that you're not
relying on enumeration which means that devices aren't going to move
around, which is always good for GRUB.  Thus, I don't think we should
invent an enumeration scheme and I certainly don't think we should
require entries in device.map to map /dev/md/home to (md0), or whatever;
that just takes us back to the bad old days.  However, we do need some
way to name the device in GRUB.

Does anyone object to this simple scheme?

  /dev/md/NAME => (md/NAME)
  all other md device name formats as before

As far as I'm aware, we don't use slashes in GRUB device names right
now, so this is a bit novel; but I wanted to minimise the chance of
clashes and confusion, and I don't believe using a slash should actually
do any harm.

Thanks,

-- 
Colin Watson                                       [cjwatson@ubuntu.com]

Re: mdadm 1.x device naming

[Vladimir 'φ-coder/phcoder' Serbinenko]

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On 07/02/2010 03:13 PM, Colin Watson wrote:
> Does anyone object to this simple scheme?
>
>   /dev/md/NAME => (md/NAME)
>   all other md device name formats as before
>
>   
I like the idea of prepending a name of subsystem to the named (and not
just numbered) devices. In retrospect lvm should have been named this
way (lvm/mylvmname).
> As far as I'm aware, we don't use slashes in GRUB device names right
> now, so this is a bit novel; but I wanted to minimise the chance of
> clashes and confusion, and I don't believe using a slash should actually
> do any harm.
>   
We already use slashes on OFW.
> Thanks,
>
>   


-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko



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Re: mdadm 1.x device naming

[martin f krafft]

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also sprach Colin Watson <cjwatson@ubuntu.com> [2010.07.02.1513 +0200]:
> Does anyone object to this simple scheme?
> 
>   /dev/md/NAME => (md/NAME)
>   all other md device name formats as before

That's what I use in the mdadm package too.

> As far as I'm aware, we don't use slashes in GRUB device names right
> now, so this is a bit novel; but I wanted to minimise the chance of
> clashes and confusion, and I don't believe using a slash should actually
> do any harm.

You could use a dash like LVM too.

And do keep in mind that named arrays still have a super-minor field
with the number, just like the 0.9 metadata ones, so you don't have
to use names. But I agree that it's better.

-- 
 .''`.   martin f. krafft <madduck@d.o>      Related projects:
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                                                    -- albert einstein

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