Clarification required about xfs_metadump and xfs_mdrestore

Clarification required about xfs_metadump and xfs_mdrestore

[murali krishna]

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Hi All,

Got your email id from Nathan Scott.

Could you please clarify the reasons behind stating below statement in
xfs_metadump man page.



*xfs_metadump should not be used for any purposes other than for
 debugging and reporting filesystem problems*
Man page: http://man7.org/linux/man-pages/man8/xfs_metadump.8.html

I am trying to encrypt my existing xfs drive (/dev/sda2) and would like to
backup metadata using xfs_metadump and restore it back using xfs_mdrestore
after encrypting my drive. In order to retain entire contents of my
realtime partition (/dev/sda1), I need to perform this step.

Can I use xfs_metadump to backup meta-data of xfs  and restore it back
successfully ?
Why xfs_metadump should be specifically used as debugging tool ? Please
clarify ?

Thanks in Advance,
Murali

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Re: Clarification required about xfs_metadump and xfs_mdrestore

[Eric Sandeen]

On 9/27/16 8:49 AM, murali krishna wrote:
> Hi All,
> 
> Got your email id from Nathan Scott. 
> 
> Could you please clarify the reasons behind stating below statement in
> xfs_metadump man page.
> 
> /xfs_metadump should not be used for any purposes other than for
>        debugging and reporting filesystem problems
> /
> Man page: http://man7.org/linux/man-pages/man8/xfs_metadump.8.html <http://man7.org/linux/man-pages/man8/xfs_metadump.8.html>

Well, that's the only thing it's designed and tested for.

> I am trying to encrypt my existing xfs drive (/dev/sda2) and would
> like to backup metadata using xfs_metadump and restore it back using
> xfs_mdrestore after encrypting my drive. In order to retain entire
> contents of my realtime partition (/dev/sda1), I need to perform this
> step.

I don't know what mechanism you plan to use for encryption, but this
sounds like a recipe for disaster.  Offhand I can't think of any existing
block device encryption method for which this would work.

> Can I use xfs_metadump to backup meta-data of xfs  and restore it back successfully ?

Probably, but we did not design it or test it for that.

> Why xfs_metadump should be specifically used as debugging tool ? Please clarify ?

Because that's what it's designed for.

You /could/ use a big wrench as a hammer, and you /might/ get the nail
in, or you might smash your fingers, bend the nail, damage the piece of
wood, or any other number of unexpected failures from using the wrong
tool for the job...  ;)

-Eric

> Thanks in Advance,
> Murali
> 
> 
> _______________________________________________
> xfs mailing list
> xfs@oss.sgi.com
> http://oss.sgi.com/mailman/listinfo/xfs
> 

Re: Clarification required about xfs_metadump and xfs_mdrestore

[Darrick J. Wong]

On Tue, Sep 27, 2016 at 09:49:11AM -0400, murali krishna wrote:
> Hi All,
> 
> Got your email id from Nathan Scott.
> 
> Could you please clarify the reasons behind stating below statement in
> xfs_metadump man page.
> 
> 
> 
> *xfs_metadump should not be used for any purposes other than for
>  debugging and reporting filesystem problems*
> Man page: http://man7.org/linux/man-pages/man8/xfs_metadump.8.html
> 
> I am trying to encrypt my existing xfs drive (/dev/sda2) and would like to
> backup metadata using xfs_metadump and restore it back using xfs_mdrestore
> after encrypting my drive. In order to retain entire contents of my
> realtime partition (/dev/sda1), I need to perform this step.
> 
> Can I use xfs_metadump to backup meta-data of xfs  and restore it back
> successfully ?
> Why xfs_metadump should be specifically used as debugging tool ? Please
> clarify ?

Uh.... if your goal is to back up data, reformat the storage with a crypto
layer, and then restore the data, why not just use xfsdump/xfsrestore?
Your data will end up all nicely defragmented, too.

--D

> 
> Thanks in Advance,
> Murali

> _______________________________________________
> xfs mailing list
> xfs@oss.sgi.com
> http://oss.sgi.com/mailman/listinfo/xfs

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Re: Clarification required about xfs_metadump and xfs_mdrestore

[Eric Sandeen]

On 9/27/16 12:04 PM, Darrick J. Wong wrote:
> On Tue, Sep 27, 2016 at 09:49:11AM -0400, murali krishna wrote:
>> Hi All,
>>
>> Got your email id from Nathan Scott.
>>
>> Could you please clarify the reasons behind stating below statement in
>> xfs_metadump man page.
>>
>>
>>
>> *xfs_metadump should not be used for any purposes other than for
>>  debugging and reporting filesystem problems*
>> Man page: http://man7.org/linux/man-pages/man8/xfs_metadump.8.html
>>
>> I am trying to encrypt my existing xfs drive (/dev/sda2) and would like to
>> backup metadata using xfs_metadump and restore it back using xfs_mdrestore
>> after encrypting my drive. In order to retain entire contents of my
>> realtime partition (/dev/sda1), I need to perform this step.
>>
>> Can I use xfs_metadump to backup meta-data of xfs  and restore it back
>> successfully ?
>> Why xfs_metadump should be specifically used as debugging tool ? Please
>> clarify ?
> 
> Uh.... if your goal is to back up data, reformat the storage with a crypto
> layer, and then restore the data, why not just use xfsdump/xfsrestore?
> Your data will end up all nicely defragmented, too.

Right, sorry - if you want to migrate to an encrypted block device, use
dump & restore.  Sorry, the metadata-restoration scheme confused me.  :)

-eric

> --D
> 
>>
>> Thanks in Advance,
>> Murali

Re: Clarification required about xfs_metadump and xfs_mdrestore

[murali krishna]

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Hi Darrick,

Thanks for the response.

Could you please clarify if there is any strong reason behind in stating to
use xfs_metadump and xfs_mdrestore as just debugging tools in their
respective man pages ?

We tried xfsdump, its backing up the rtdev partition (/dev/sda1) as well. I
have around 450GB worth of recordings in my /dev/sda1 (rtdev).
I don't want to use any intermediate storage to backup all these data.

Yes, my aim is to backup the metadata (dont want to touch my rtdev) on
/dev/sda2, reformat "/dev/sda2"  with crypt layer, restore metadata back on
/dev/sda2.
At the end, I am expecting my rtdev untouched and should automatically
appear after encrypting my /dev/sda2.

Note:
/dev/sda2- xfs partition
/dev/sda1 - xfs realtime partition

Thank you,
Murali

On Tue, Sep 27, 2016 at 1:04 PM, Darrick J. Wong <darrick.wong@oracle.com>
wrote:

> On Tue, Sep 27, 2016 at 09:49:11AM -0400, murali krishna wrote:
> > Hi All,
> >
> > Got your email id from Nathan Scott.
> >
> > Could you please clarify the reasons behind stating below statement in
> > xfs_metadump man page.
> >
> >
> >
> > *xfs_metadump should not be used for any purposes other than for
> >  debugging and reporting filesystem problems*
> > Man page: http://man7.org/linux/man-pages/man8/xfs_metadump.8.html
> >
> > I am trying to encrypt my existing xfs drive (/dev/sda2) and would like
> to
> > backup metadata using xfs_metadump and restore it back using
> xfs_mdrestore
> > after encrypting my drive. In order to retain entire contents of my
> > realtime partition (/dev/sda1), I need to perform this step.
> >
> > Can I use xfs_metadump to backup meta-data of xfs  and restore it back
> > successfully ?
> > Why xfs_metadump should be specifically used as debugging tool ? Please
> > clarify ?
>
> Uh.... if your goal is to back up data, reformat the storage with a crypto
> layer, and then restore the data, why not just use xfsdump/xfsrestore?
> Your data will end up all nicely defragmented, too.
>
> --D
>
> >
> > Thanks in Advance,
> > Murali
>
> > _______________________________________________
> > xfs mailing list
> > xfs@oss.sgi.com
> > http://oss.sgi.com/mailman/listinfo/xfs
>
>

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Re: Clarification required about xfs_metadump and xfs_mdrestore

[Dave Chinner]

On Tue, Sep 27, 2016 at 01:27:12PM -0400, murali krishna wrote:
> Hi Darrick,
> 
> Thanks for the response.
> 
> Could you please clarify if there is any strong reason behind in stating to
> use xfs_metadump and xfs_mdrestore as just debugging tools in their
> respective man pages ?

The man page is simply stating the truth - metadump/restore are
debugging tools used by XFS developers for obtaining information
required for forensic analysis of filesystem failures.

What you are wanting to do will not work, is not supported, and you
get to keep all the broken bits to yourself if you try it.
Every XFS developer you ask will say the same thing:
xfsdump/encrypt/mkfs/xfs_restore is the only way to do what you want
to do.

-Dave.
-- 
Dave Chinner
david@fromorbit.com

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Re: Clarification required about xfs_metadump and xfs_mdrestore

[murali krishna]

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Hi Dave,

Thanks for the clarification and inputs. Your support is much appreciated.

Murali

On Tue, Sep 27, 2016 at 5:41 PM, Dave Chinner <david@fromorbit.com> wrote:

> On Tue, Sep 27, 2016 at 01:27:12PM -0400, murali krishna wrote:
> > Hi Darrick,
> >
> > Thanks for the response.
> >
> > Could you please clarify if there is any strong reason behind in stating
> to
> > use xfs_metadump and xfs_mdrestore as just debugging tools in their
> > respective man pages ?
>
> The man page is simply stating the truth - metadump/restore are
> debugging tools used by XFS developers for obtaining information
> required for forensic analysis of filesystem failures.
>
> What you are wanting to do will not work, is not supported, and you
> get to keep all the broken bits to yourself if you try it.
> Every XFS developer you ask will say the same thing:
> xfsdump/encrypt/mkfs/xfs_restore is the only way to do what you want
> to do.
>
> -Dave.
> --
> Dave Chinner
> david@fromorbit.com
>

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