Placing the root partition on an XFS filesystem is not supported

Placing the root partition on an XFS filesystem is not supported

[Marcos Mello]

http://git.fedorahosted.org/git/?p=anaconda.git;a=commit;h=b3e19d43840f6c4015fab75411853003fcf26a63

Does someone knows why? I'm trying to get rid of EXT* partitions on my new
CentOS 6.2 installs but apparently it will not be possible.

Marcos

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Re: Placing the root partition on an XFS filesystem is not supported

[Stan Hoeppner]

On 1/29/2012 6:46 AM, Marcos Mello wrote:
> http://git.fedorahosted.org/git/?p=anaconda.git;a=commit;h=b3e19d43840f6c4015fab75411853003fcf26a63
> 
> Does someone knows why? I'm trying to get rid of EXT* partitions on my new
> CentOS 6.2 installs but apparently it will not be possible.

I'm unsure what this Fedora commit is all about, but in the general
Linux case you can put root on XFS, with a minor caveat.  See:

http://www.xfs.org/index.php/XFS_FAQ#Q:_Can_XFS_be_used_for_a_root_filesystem.3F

-- 
Stan

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Re: Placing the root partition on an XFS filesystem is not supported

[Marcos Mello]

Stan Hoeppner <stan <at> hardwarefreak.com> writes:

> 
> On 1/29/2012 6:46 AM, Marcos Mello wrote:
> >
http://git.fedorahosted.org/git/?p=anaconda.git;a=commit;h=b3e19d43840f6c4015fab75411853003fcf26a63
> > 
> > Does someone knows why? I'm trying to get rid of EXT* partitions on my new
> > CentOS 6.2 installs but apparently it will not be possible.
> 
> I'm unsure what this Fedora commit is all about, but in the general
> Linux case you can put root on XFS, with a minor caveat.  See:
> 
> http://www.xfs.org/index.php/XFS_FAQ#Q:_Can_XFS_be_used_for_a_root_filesystem.3F
> 

Yeah, some time ago I run XFS as my / on Arch. But Anaconda doesn't allow it
now. So we're still forced to have an EXT partition for the root filesystem in
the Red Hat land.

Found this
http://pastebin.com/gHqGGkSp

Marcos

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Re: Placing the root partition on an XFS filesystem is not supported

[Eric Sandeen]

On 1/29/12 6:46 AM, Marcos Mello wrote:
> http://git.fedorahosted.org/git/?p=anaconda.git;a=commit;h=b3e19d43840f6c4015fab75411853003fcf26a63
> 
> Does someone knows why? I'm trying to get rid of EXT* partitions on my new
> CentOS 6.2 installs but apparently it will not be possible.

Was done for RHEL, AFAIK.

In general there is no problem with xfs on a root partition.  However, the installer
may not make it easy or available for you.

(I never use xfs for /boot though, I don't trust grub enough for that honestly).

-Eric

> Marcos
> 
> _______________________________________________
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> 

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Re: Placing the root partition on an XFS filesystem is not supported

[Marcos Mello]

Eric Sandeen <sandeen <at> sandeen.net> writes:

> 
> In general there is no problem with xfs on a root partition.  However, the
installer
> may not make it easy or available for you.
> 
> (I never use xfs for /boot though, I don't trust grub enough for that
honestly).
> 
> -Eric

Same thing on Fedora 16. Let's hope some day Anaconda will change that.

About GRUB with a XFS /boot the problem was with GRUB Lagacy, wasn't it?
Or GRUB2 is still buggy?

Marcos

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Re: Placing the root partition on an XFS filesystem is not supported

[Eric Sandeen]

On 2/3/12 8:39 AM, Marcos Mello wrote:
> Eric Sandeen <sandeen <at> sandeen.net> writes:
> 
>>
>> In general there is no problem with xfs on a root partition.  However, the
> installer
>> may not make it easy or available for you.
>>
>> (I never use xfs for /boot though, I don't trust grub enough for that
> honestly).
>>
>> -Eric
> 
> Same thing on Fedora 16. Let's hope some day Anaconda will change that.

F16 prevents it?  I didn't see it in the upstream tree.  That should
not be so.  :/

> About GRUB with a XFS /boot the problem was with GRUB Lagacy, wasn't it?
> Or GRUB2 is still buggy?

I have no idea, actually.  I delved into grub a bit, it was disturbing
enough that I have not tried to look at grub2.  :)

-Eric

> Marcos
> 
> _______________________________________________
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> 

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Re: Placing the root partition on an XFS filesystem is not supported

[Dave Chinner]

On Fri, Feb 03, 2012 at 12:50:17PM -0600, Eric Sandeen wrote:
> On 2/3/12 8:39 AM, Marcos Mello wrote:
> > Eric Sandeen <sandeen <at> sandeen.net> writes:
> > 
> >>
> >> In general there is no problem with xfs on a root partition.  However, the
> > installer
> >> may not make it easy or available for you.
> >>
> >> (I never use xfs for /boot though, I don't trust grub enough for that
> > honestly).
> >>
> >> -Eric
> > 
> > Same thing on Fedora 16. Let's hope some day Anaconda will change that.
> 
> F16 prevents it?  I didn't see it in the upstream tree.  That should
> not be so.  :/
> 
> > About GRUB with a XFS /boot the problem was with GRUB Lagacy, wasn't it?
> > Or GRUB2 is still buggy?
> 
> I have no idea, actually.  I delved into grub a bit, it was disturbing
> enough that I have not tried to look at grub2.  :)

Certainly the problem exists with legacy grub - it assumes that it
can write to the first sector or any disk or partition which
overwrites the XFS superblock...

The grub2 manual:

http://www.gnu.org/software/grub/manual/grub.html#BIOS-installation

indicates that if you are using BIOS/MBR based booting, then grub2
still writes to the first sector of the partition that contains the
grub directory to install the stage 1.5 loader.  Indeed:

"boot.img

On PC BIOS systems, this image is the first part of GRUB to start.
It is written to a master boot record (MBR) or to the boot sector of
a partition. Because a PC boot sector is 512 bytes, the size of this
image is exactly 512 bytes. 

The sole function of boot.img is to read the first sector of the
core image from a local disk and jump to it. Because of the size
restriction, boot.img cannot understand any file system structure,
so grub-setup hardcodes the location of the first sector of the core
image into boot.img when installing GRUB. "

IOWs, you have to treat grub2 identically to legacy grub in that it
thinks it owns the first sector of any partition on the disk.
Therefore, you need a separate /boot partition that is not formated
with XFS to be safe.

There's a reason I went back to using LILO....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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Re: Placing the root partition on an XFS filesystem is not supported

[Eric Sandeen]

On 2/5/12 6:11 PM, Dave Chinner wrote:
> On Fri, Feb 03, 2012 at 12:50:17PM -0600, Eric Sandeen wrote:
>> On 2/3/12 8:39 AM, Marcos Mello wrote:
>>> Eric Sandeen <sandeen <at> sandeen.net> writes:
>>>
>>>>
>>>> In general there is no problem with xfs on a root partition.  However, the
>>> installer
>>>> may not make it easy or available for you.
>>>>
>>>> (I never use xfs for /boot though, I don't trust grub enough for that
>>> honestly).
>>>>
>>>> -Eric
>>>
>>> Same thing on Fedora 16. Let's hope some day Anaconda will change that.
>>
>> F16 prevents it?  I didn't see it in the upstream tree.  That should
>> not be so.  :/
>>
>>> About GRUB with a XFS /boot the problem was with GRUB Lagacy, wasn't it?
>>> Or GRUB2 is still buggy?
>>
>> I have no idea, actually.  I delved into grub a bit, it was disturbing
>> enough that I have not tried to look at grub2.  :)
> 
> Certainly the problem exists with legacy grub - it assumes that it
> can write to the first sector or any disk or partition which
> overwrites the XFS superblock...

well, it was worse than that.  I can work around the grub-on-a-partition
problem, but what I ran into was grub reading & writing to/from the block
device under a mounted filesystem - corruption and hilarity ensued.

-Eric

> The grub2 manual:
> 
> http://www.gnu.org/software/grub/manual/grub.html#BIOS-installation
> 
> indicates that if you are using BIOS/MBR based booting, then grub2
> still writes to the first sector of the partition that contains the
> grub directory to install the stage 1.5 loader.  Indeed:
> 
> "boot.img
> 
> On PC BIOS systems, this image is the first part of GRUB to start.
> It is written to a master boot record (MBR) or to the boot sector of
> a partition. Because a PC boot sector is 512 bytes, the size of this
> image is exactly 512 bytes. 
> 
> The sole function of boot.img is to read the first sector of the
> core image from a local disk and jump to it. Because of the size
> restriction, boot.img cannot understand any file system structure,
> so grub-setup hardcodes the location of the first sector of the core
> image into boot.img when installing GRUB. "
> 
> IOWs, you have to treat grub2 identically to legacy grub in that it
> thinks it owns the first sector of any partition on the disk.
> Therefore, you need a separate /boot partition that is not formated
> with XFS to be safe.
> 
> There's a reason I went back to using LILO....
> 
> Cheers,
> 
> Dave.

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Re: Placing the root partition on an XFS filesystem is not supported

[Dave Chinner]

On Sun, Feb 05, 2012 at 06:13:28PM -0600, Eric Sandeen wrote:
> On 2/5/12 6:11 PM, Dave Chinner wrote:
> > On Fri, Feb 03, 2012 at 12:50:17PM -0600, Eric Sandeen wrote:
> >> On 2/3/12 8:39 AM, Marcos Mello wrote:
> >>> Eric Sandeen <sandeen <at> sandeen.net> writes:
> >>>
> >>>>
> >>>> In general there is no problem with xfs on a root partition.  However, the
> >>> installer
> >>>> may not make it easy or available for you.
> >>>>
> >>>> (I never use xfs for /boot though, I don't trust grub enough for that
> >>> honestly).
> >>>>
> >>>> -Eric
> >>>
> >>> Same thing on Fedora 16. Let's hope some day Anaconda will change that.
> >>
> >> F16 prevents it?  I didn't see it in the upstream tree.  That should
> >> not be so.  :/
> >>
> >>> About GRUB with a XFS /boot the problem was with GRUB Lagacy, wasn't it?
> >>> Or GRUB2 is still buggy?
> >>
> >> I have no idea, actually.  I delved into grub a bit, it was disturbing
> >> enough that I have not tried to look at grub2.  :)
> > 
> > Certainly the problem exists with legacy grub - it assumes that it
> > can write to the first sector or any disk or partition which
> > overwrites the XFS superblock...
> 
> well, it was worse than that.  I can work around the grub-on-a-partition
> problem, but what I ran into was grub reading & writing to/from the block
> device under a mounted filesystem - corruption and hilarity ensued.

Oh, grub2 does worse things than that - grub_probe mounts any device
that appears to have a valid superblock so it can find out what
devices it needs to list in it's boot menu. I found this out when I
built a big DM stripe out of disks that used to have filesystems on
them.  grub-probe mounted every single device -inside- the stripe
and ran log recovery on them, corrupting the new filesystem and
quite a bit of data on the DM stripe they were part of....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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Re: Placing the root partition on an XFS filesystem is not supported

[Eric Sandeen]

On 2/5/12 7:54 PM, Dave Chinner wrote:
> On Sun, Feb 05, 2012 at 06:13:28PM -0600, Eric Sandeen wrote:
>> On 2/5/12 6:11 PM, Dave Chinner wrote:
>>> On Fri, Feb 03, 2012 at 12:50:17PM -0600, Eric Sandeen wrote:
>>>> On 2/3/12 8:39 AM, Marcos Mello wrote:
>>>>> Eric Sandeen <sandeen <at> sandeen.net> writes:
>>>>>
>>>>>>
>>>>>> In general there is no problem with xfs on a root partition.  However, the
>>>>> installer
>>>>>> may not make it easy or available for you.
>>>>>>
>>>>>> (I never use xfs for /boot though, I don't trust grub enough for that
>>>>> honestly).
>>>>>>
>>>>>> -Eric
>>>>>
>>>>> Same thing on Fedora 16. Let's hope some day Anaconda will change that.
>>>>
>>>> F16 prevents it?  I didn't see it in the upstream tree.  That should
>>>> not be so.  :/
>>>>
>>>>> About GRUB with a XFS /boot the problem was with GRUB Lagacy, wasn't it?
>>>>> Or GRUB2 is still buggy?
>>>>
>>>> I have no idea, actually.  I delved into grub a bit, it was disturbing
>>>> enough that I have not tried to look at grub2.  :)
>>>
>>> Certainly the problem exists with legacy grub - it assumes that it
>>> can write to the first sector or any disk or partition which
>>> overwrites the XFS superblock...
>>
>> well, it was worse than that.  I can work around the grub-on-a-partition
>> problem, but what I ran into was grub reading & writing to/from the block
>> device under a mounted filesystem - corruption and hilarity ensued.
> 
> Oh, grub2 does worse things than that - grub_probe mounts any device
> that appears to have a valid superblock so it can find out what
> devices it needs to list in it's boot menu. I found this out when I
> built a big DM stripe out of disks that used to have filesystems on
> them.  grub-probe mounted every single device -inside- the stripe
> and ran log recovery on them, corrupting the new filesystem and
> quite a bit of data on the DM stripe they were part of....

Ok, your horror story wins from a pain POV ;)

but sounds like someone should have zeroed out a bit more disk
when setting up the dm stripes :(

I've always thought maybe we needed a libzero.so to zap every known signature
on disk....

-Eric

> Cheers,
> 
> Dave.

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Re: Placing the root partition on an XFS filesystem is not supported

[Stan Hoeppner]

On 2/5/2012 7:58 PM, Eric Sandeen wrote:
> On 2/5/12 7:54 PM, Dave Chinner wrote:

>> Oh, grub2 does worse things than that - grub_probe mounts any device
>> that appears to have a valid superblock so it can find out what
>> devices it needs to list in it's boot menu. I found this out when I
>> built a big DM stripe out of disks that used to have filesystems on
>> them.  grub-probe mounted every single device -inside- the stripe
>> and ran log recovery on them, corrupting the new filesystem and
>> quite a bit of data on the DM stripe they were part of....
> 
> Ok, your horror story wins from a pain POV ;)

What's the default bootloader of RHEL/Fedora?  I'm not asking
rhetorically.  I've never used either, and I'm curios if Red Hat went
the grub/grub2 route like SuSE and many/most other distros.

I use strictly Debian/LILO myself.  I was quite relieved when they
decided not to throw LILO out of the distro.  Apparently it had been
abandoned upstream.  Luckily another dev took ownership at the last minute.

-- 
Stan

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Re: Placing the root partition on an XFS filesystem is not supported

[Marcos Mello]

Eric Sandeen <sandeen <at> sandeen.net> writes:

> On 2/5/12 7:54 PM, Dave Chinner wrote:
> > On Sun, Feb 05, 2012 at 06:13:28PM -0600, Eric Sandeen wrote:
> >> On 2/5/12 6:11 PM, Dave Chinner wrote:
<snip>
> >>
> >> well, it was worse than that.  I can work around the grub-on-a-partition
> >> problem, but what I ran into was grub reading & writing to/from the block
> >> device under a mounted filesystem - corruption and hilarity ensued.
> > 
> > Oh, grub2 does worse things than that - grub_probe mounts any device
> > that appears to have a valid superblock so it can find out what
> > devices it needs to list in it's boot menu. I found this out when I
> > built a big DM stripe out of disks that used to have filesystems on
> > them.  grub-probe mounted every single device -inside- the stripe
> > and ran log recovery on them, corrupting the new filesystem and
> > quite a bit of data on the DM stripe they were part of....
> 
> Ok, your horror story wins from a pain POV ;)
> 
> but sounds like someone should have zeroed out a bit more disk
> when setting up the dm stripes :(
> 
> I've always thought maybe we needed a libzero.so to zap every known signature
> on disk....
> 

Thanks a lot for the explanation folks! It would be nice have this documented on
the XFS FAQ
http://xfs.org/index.php/XFS_FAQ#Q:_Does_GRUB_work_with_XFS.3F

Eric, landed recently in util-linux's libblkid a function for that AFAIK
http://git.kernel.org/?p=utils/util-linux/util-linux.git;a=commitdiff;h=2b89be6c802bdbdf6830dbd060c96e33f179b135

Marcos

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Re: Placing the root partition on an XFS filesystem is not supported

[Richard Scobie]

Eric Sandeen wrote:

 > F16 prevents it?  I didn't see it in the upstream tree.  That should
 > not be so.  :/

Indeed not. I completed an F16 install 4 days ago, using XFS as the / 
filesystem.

Regards,

Richard

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Re: Placing the root partition on an XFS filesystem is not supported

[Marcos Mello]

Richard Scobie <r.scobie <at> clear.net.nz> writes:

> 
> Eric Sandeen wrote:
> 
>  > F16 prevents it?  I didn't see it in the upstream tree.  That should
>  > not be so.  :/
> 
> Indeed not. I completed an F16 install 4 days ago, using XFS as the / 
> filesystem.
> 

:-| Well, I'm amlost sure I got the same message when intalling F16 minimal ISO
last week. Will try again, maybe was just a confusion from my part.

Thanks,

Marcos

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Re: Placing the root partition on an XFS filesystem is not supported

[Eric Sandeen]

On Feb 4, 2012, at 8:29 AM, Marcos Mello <marcosfrm@gmail.com> wrote:

> Richard Scobie <r.scobie <at> clear.net.nz> writes:
> 
>> 
>> Eric Sandeen wrote:
>> 
>>> F16 prevents it?  I didn't see it in the upstream tree.  That should
>>> not be so.  :/
>> 
>> Indeed not. I completed an F16 install 4 days ago, using XFS as the / 
>> filesystem.
>> 
> 
> :-| Well, I'm amlost sure I got the same message when intalling F16 minimal ISO
> last week. Will try again, maybe was just a confusion from my part.
> 
Note, the livecd cannot do an xfs install because it just transfers the (ext4) livecd root to the hard drive.  The non-livecd installer should work though.

-Eric

> Thanks,
> 
> Marcos
> 
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