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Old 05-06-2011, 05:44 PM
 
Default grub-probe: error: cannot stat `/dev/root'

This just started after my most recent (very painful) dist-upgrade. It seems that BTRFS is not compatible with grub and Debian. I very nearly lost my whole system because of this catastrophe.

Does anyone know the nature of the error and how to fix?


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Old 05-07-2011, 10:57 AM
Camaleón
 
Default grub-probe: error: cannot stat `/dev/root'

On Fri, 06 May 2011 10:44:21 -0700, CACook wrote:

> This just started after my most recent (very painful) dist-upgrade. It
> seems that BTRFS is not compatible with grub and Debian. I very nearly
> lost my whole system because of this catastrophe.
>
> Does anyone know the nature of the error and how to fix?

You're asking for so much :-)

First, the btrfs filesystem is still very experimental so only use it if
you really (I mean *really*) know what you are doing and also know how to
deal when things go wrong. I would even expect data loss (directly or
indirectly related to the usage of this filesystem) so make daily backups
if needed.

Second, write a bug report at Debian BTS. Every distribution applies
different patches/quirks for GRUB and that can make a difference (meaning
that the issue can be only visible in Debian based distros while it does
not present in others).

And third, where are you getting the above error (at booting, when
running grub-something...?).

Greetings,

--
Camaleón


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Old 05-07-2011, 02:04 PM
"Boyd Stephen Smith Jr."
 
Default grub-probe: error: cannot stat `/dev/root'

In <pan.2011.05.07.10.57.16@gmail.com>, Camaleón wrote:
>On Fri, 06 May 2011 10:44:21 -0700, CACook wrote:
>> This just started after my most recent (very painful) dist-upgrade. It
>> seems that BTRFS is not compatible with grub and Debian. I very nearly
>> lost my whole system because of this catastrophe.
>>
>> Does anyone know the nature of the error and how to fix?
>
>You're asking for so much :-)
>
>First, the btrfs filesystem is still very experimental so only use it if
>you really (I mean *really*) know what you are doing and also know how to
>deal when things go wrong. I would even expect data loss (directly or
>indirectly related to the usage of this filesystem) so make daily backups
>if needed.

As a current btrfs user, I don't recommend you run it on the Squeeze kernel
(2.6.32-5) because there are certain circumstances where it doesn't gracefully
handle out-of-space issues and that "df" reports for it lie. I recently filed
a bug against the Debian kernel due to this; two BUG() calls within a second
leading to a broken btrfs module and needing a reboot and some manual file
system recovery.

I don't recommend you use the Wheezy kernel (2.6.38-2 in the package name;
2.6.38-3 in the package version) either. There's a least one outstanding bug
that I filed involving the in-kernel NULL pointer dereference while mounting a
btrfs file system. Again, this leads to a broken btrfs module and needs a
reboot to fix. However, it happens easy enough and consistently enough during
the Debian boot process that it effectively makes that kernel unusable.

I've not tested the Sid kernel; I may do that today.

I thought 2.6.39-rc4 from experimental would work, but they haven't put the
2.6.39 kbuild infrastructure in experimental and I have an out-of-tree kernel
module that I need for daily operations. This is a close second just because
I don't have any experience with it, yet.

Right now, my data losses due to btrfs, if any, are still unnoticed. However,
I am more worried than ever before that I won't find a file system that meets
my unique needs before I start losing data. My unique needs are: on-line
growing, on- or off-line shrinking, good performance on 4+ TiB file systems
with less than 4 GiB free space. For the few file systems I haven't converted
to btrfs, I am still using reiserfs.

FWIW, I don't think GRUB2 has BtrFS support, yet. So, you'd have to store
your kernel and initrd on a different file system.
--
Boyd Stephen Smith Jr. ,= ,-_-. =.
bss@iguanasuicide.net ((_/)o o(\_))
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Old 05-07-2011, 02:54 PM
"Boyd Stephen Smith Jr."
 
Default grub-probe: error: cannot stat `/dev/root'

In <201105070904.26205.bss@iguanasuicide.net>, Boyd Stephen Smith Jr. wrote:
>In <pan.2011.05.07.10.57.16@gmail.com>, Camaleón wrote:
>>On Fri, 06 May 2011 10:44:21 -0700, CACook wrote:
>>> This just started after my most recent (very painful) dist-upgrade. It
>>> seems that BTRFS is not compatible with grub and Debian. I very nearly
>>> lost my whole system because of this catastrophe.
>>>
>>> Does anyone know the nature of the error and how to fix?
>>
>>You're asking for so much :-)
>>
>>First, the btrfs filesystem is still very experimental so only use it if
>>you really (I mean *really*) know what you are doing and also know how to
>>deal when things go wrong. I would even expect data loss (directly or
>>indirectly related to the usage of this filesystem) so make daily backups
>>if needed.
>
>As a current btrfs user, I don't recommend you run it on the Squeeze kernel
>(2.6.32-5) because

Bug 625899

>I don't recommend you use the Wheezy kernel (2.6.38-2 in the package name;
>2.6.38-3 in the package version) either. There's a least one outstanding
>bug

Bug 622218

>I've not tested the Sid kernel; I may do that today.

Just tested. Also affected by bug 622218.

>I thought 2.6.39-rc5 from experimental would work, but they haven't put the
>2.6.39 kbuild infrastructure in experimental and I have an out-of-tree
>kernel module that I need for daily operations. This is a close second
>just because I don't have any experience with it, yet.

You could try this one, if you aren't using any out-of-tree modules. For me
it is the NVidia module. I really should find the money for a cheap ATI card
so I can use FLOSS modules.
--
Boyd Stephen Smith Jr. ,= ,-_-. =.
bss@iguanasuicide.net ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-'
http://iguanasuicide.net/ \_/
 
Old 05-08-2011, 08:08 AM
Andrei Popescu
 
Default grub-probe: error: cannot stat `/dev/root'

On Sb, 07 mai 11, 09:54:37, Boyd Stephen Smith Jr. wrote:
>
> You could try this one, if you aren't using any out-of-tree modules. For me
> it is the NVidia module. I really should find the money for a cheap ATI card
> so I can use FLOSS modules.

And nouveau?

Regards,
Andrei
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Old 05-08-2011, 12:55 PM
 
Default grub-probe: error: cannot stat `/dev/root'

On Saturday 7 May, 2011 07:04:16 Boyd Stephen Smith Jr. wrote:
> As a current btrfs user, I don't recommend you run it on the Squeeze kernel
> (2.6.32-5) because there are certain circumstances where it doesn't gracefully
> handle out-of-space issues and that "df" reports for it lie. I recently filed
> a bug against the Debian kernel due to this; two BUG() calls within a second
> leading to a broken btrfs module and needing a reboot and some manual file
> system recovery.

Wow, yeah. For having been years in development and fully financially supported by Oracle, this filesystem is a trainwreck. I'm ditching it.

But I did submit a bug by email on grub-pc.

What a mess. Scary.


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Old 05-08-2011, 02:59 PM
Camaleón
 
Default grub-probe: error: cannot stat `/dev/root'

On Sun, 08 May 2011 05:55:18 -0700, CACook wrote:

> On Saturday 7 May, 2011 07:04:16 Boyd Stephen Smith Jr. wrote:
>> As a current btrfs user, I don't recommend you run it on the Squeeze
>> kernel (2.6.32-5) because there are certain circumstances where it
>> doesn't gracefully handle out-of-space issues and that "df" reports for
>> it lie. I recently filed a bug against the Debian kernel due to this;
>> two BUG() calls within a second leading to a broken btrfs module and
>> needing a reboot and some manual file system recovery.
>
> Wow, yeah. For having been years in development

It's only two years (!). We can say it's just "a baby" compared to the
dinosaurs of ext2/3, reiserfs and xfs :-)

> and fully financially supported by Oracle,

Well, afterall is a GPL project.

> this filesystem is a trainwreck.

I'd say it's under development which means not suitable for production
systems.

> I'm ditching it.

Nowadays you can use it on a testing computer. Beyond that, you risk to
expose your data to almost any thing.

> But I did submit a bug by email on grub-pc.
>
> What a mess. Scary.

Greetings,

--
Camaleón


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Old 05-08-2011, 05:09 PM
"Boyd Stephen Smith Jr."
 
Default grub-probe: error: cannot stat `/dev/root'

In <20110508080807.GC7081@think.nuvreauspam>, Andrei Popescu wrote:
>On Sb, 07 mai 11, 09:54:37, Boyd Stephen Smith Jr. wrote:
>> You could try this one, if you aren't using any out-of-tree modules. For
>> me it is the NVidia module. I really should find the money for a cheap
>> ATI card so I can use FLOSS modules.
>
>And nouveau?

I actually haven't tried it, yet. However the "nv" driver was utterly
unusable. I use desktop effects across multiple monitors, and TwinView
appears to be the only way to get any acceleration out of that kind of set up.

I'll give Nouveau a chance sometime this week.
--
Boyd Stephen Smith Jr. ,= ,-_-. =.
bss@iguanasuicide.net ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-'
http://iguanasuicide.net/ \_/
 

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