regarding journaling mode

regarding journaling mode

[Rakesh Patel]

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Hi,

I come to know XFS is using writeback journaling mode. As per the
journaling guide, writeback is unsafe which does not preserve data and
metadata write synchronization.

I really want to know reason behind to choose writeback mode for journaling
in XFS.



Thanks.
Regards,
Rakesh

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Re: regarding journaling mode

[Dave Chinner]

On Mon, Jul 06, 2015 at 11:38:32AM +0530, Rakesh Patel wrote:
> Hi,
> 
> I come to know XFS is using writeback journaling mode.

Can you explain how you came to that conclusion?

> As per the
> journaling guide, writeback is unsafe which does not preserve data and
> metadata write synchronization.

What journalling guide would that be? Please quote your sources when
asking questions.

> I really want to know reason behind to choose writeback mode for journaling
> in XFS.

Metadata updates after data IO completion are used instead of
ordering data writeback operations through the journal.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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RE: regarding journaling mode

[rakesh patel]

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How metadata is committed only after data? Is there any other file system feature? Because write back mode does not preserve it?

Rakesh

-----Original Message-----
From: "Dave Chinner" <david@fromorbit.com>
Sent: ‎07-‎07-‎2015 05:59
To: "Rakesh Patel" <patelrakeshcomp@gmail.com>
Cc: "xfs@oss.sgi.com" <xfs@oss.sgi.com>
Subject: Re: regarding journaling mode

On Mon, Jul 06, 2015 at 11:38:32AM +0530, Rakesh Patel wrote:
> Hi,
> 
> I come to know XFS is using writeback journaling mode.

Can you explain how you came to that conclusion?

> As per the
> journaling guide, writeback is unsafe which does not preserve data and
> metadata write synchronization.

What journalling guide would that be? Please quote your sources when
asking questions.

> I really want to know reason behind to choose writeback mode for journaling
> in XFS.

Metadata updates after data IO completion are used instead of
ordering data writeback operations through the journal.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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RE: regarding journaling mode

[rakesh patel]

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How Metadata updates after data IO completion done? Write back mode does not support synchronization?

Is there any other feature ??

-----Original Message-----
From: "Dave Chinner" <david@fromorbit.com>
Sent: ‎07-‎07-‎2015 05:59
To: "Rakesh Patel" <patelrakeshcomp@gmail.com>
Cc: "xfs@oss.sgi.com" <xfs@oss.sgi.com>
Subject: Re: regarding journaling mode

On Mon, Jul 06, 2015 at 11:38:32AM +0530, Rakesh Patel wrote:
> Hi,
> 
> I come to know XFS is using writeback journaling mode.

Can you explain how you came to that conclusion?

> As per the
> journaling guide, writeback is unsafe which does not preserve data and
> metadata write synchronization.

What journalling guide would that be? Please quote your sources when
asking questions.

> I really want to know reason behind to choose writeback mode for journaling
> in XFS.

Metadata updates after data IO completion are used instead of
ordering data writeback operations through the journal.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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Re: regarding journaling mode

[Rakesh Patel]

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https://www.kernel.org/doc/Documentation/filesystems/ext4.txt

data=writeback		Data ordering is not preserved, data may be written
			into the main file system after its metadata has been
			committed to the journal.


Rakesh

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Re: regarding journaling mode

[Jan Kara]

On Thu 09-07-15 10:18:55, Rakesh Patel wrote:
> https://www.kernel.org/doc/Documentation/filesystems/ext4.txt
> 
> data=writeback		Data ordering is not preserved, data may be written
> 			into the main file system after its metadata has been
> 			committed to the journal.

But this is about ext4, not xfs. XFS works differently and provides
necessary data safety guarantees.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

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Re: regarding journaling mode

[Rakesh Patel]

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Ok. Thanks for your information.


On Thu, Jul 9, 2015 at 2:16 PM, Jan Kara <jack@suse.cz> wrote:

> On Thu 09-07-15 10:18:55, Rakesh Patel wrote:
> > https://www.kernel.org/doc/Documentation/filesystems/ext4.txt
> >
> > data=writeback                Data ordering is not preserved, data may
> be written
> >                       into the main file system after its metadata has
> been
> >                       committed to the journal.
>
> But this is about ext4, not xfs. XFS works differently and provides
> necessary data safety guarantees.
>
>                                                                 Honza
> --
> Jan Kara <jack@suse.cz>
> SUSE Labs, CR
>

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Re: regarding journaling mode

[Emmanuel Florac]

Le Thu, 9 Jul 2015 10:18:55 +0530
Rakesh Patel <patelrakeshcomp@gmail.com> écrivait:

> https://www.kernel.org/doc/Documentation/filesystems/ext4.txt
> 
> data=writeback		Data ordering is not preserved, data
> may be written into the main file system after its metadata has been
> 			committed to the journal.

First, this is ext4, not xfs. However XFS behaves the same way, that
is, it may update metadata BEFORE the data has been committed to disk.
This has been the standard behaviour of all filesystems since linux
2.6.30 I guess.

If you're interested in the details, search for O_PONIES on the web...

-- 
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                    |   Intellique
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