linux-kernel - Re: Linux mdadm superblock question.

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Message-ID: <4877c76c1002140038p4a7d8d75r3bc9d615b0e68199@mail.gmail.com>
Date:	Sun, 14 Feb 2010 00:38:58 -0800
From:	Michael Evans <mjevans1983@...il.com>
To:	david@...g.hm
Cc:	Volker Armin Hemmann <volkerarmin@...glemail.com>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org
Subject: Re: Linux mdadm superblock question.

On Sat, Feb 13, 2010 at 11:21 PM,  <david@...g.hm> wrote:
> On Sat, 13 Feb 2010, Michael Evans wrote:
>
>> On Sat, Feb 13, 2010 at 5:51 PM, Volker Armin Hemmann
>> <volkerarmin@...glemail.com> wrote:
>>>>
>>>> 0.90 has a very bad problem, which is that it is hard to distinguish
>>>> between a RAID partition at the end of volume and a full RAID device.
>>>> This is because 0.90 doesn't actually tell you the start of the device.
>>>>
>>>> Then, of course, there are a lot of limitations on size, number of
>>>> devices, and so on in 0.90.
>>>
>>> but it is the only format supporting autodetection.
>>>
>>> So - when will autodetection be introduced with 1.X? And if not, why not?
>>>
>>> All I found was 'autodetection might be troublesome' and nothing else.
>>>  But dealing with initrds is troublesome too. Pure evil even.
>>>
>>> Gl?ck Auf,
>>> Volker
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>>
>> I remember hearing that 1.x had /no/ plans for kernel level
>> auto-detection ever.  That can be accomplished in early-userspace
>> leaving the code in the kernel much less complex, and therefore far
>> more reliable.
>>
>> In other words, 'auto-detection' for 1.x format devices is using an
>> initrd/initramfs.
>
> hmm, I've used 1.x formats without an initrd/initramfs (and without any
> conifg file on the server) and have had no problem with them being
> discovered. I haven't tried to use one for a boot/root device, so that may
> be the difference.
>
> David Lang

Yes, that is the difference.  You must have a more traditional simple
block device and filesystem drivers compiled in.  You have no need for
extra drivers or higher level device detection and evaluation (with
user-set policies to determine operation).  Anything past root-fs
mount can happen in normal user-space before logins are enabled.
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