[Ocfs2-users] ocfs2 vs ext3?

[Joel Becker]

On Fri, May 01, 2009 at 08:55:21PM +1000, Andrew (Anything) wrote:
> > echo 'stats'|debugfs.ocfs2 /dev/sdX|grep "Incompat"
> 
> I re-read your reply with the Incompat flag check and it made me think to
> check what mine were showing.
> 
> I found that my format with max-features meant that it wasn't using all the
> available features.
> Some are probably quite important for performance.
> 
> mkfs.ocfs2 -T mail --fs-feature-level=max-features /dev/sda
> debugfs.ocfs2 stats was showing:
>         Feature Compat: 1 BackupSuper
>         Feature Incompat: 272 Sparse ExtendedSlotMap
> 
> I downloaded the ocfs2-tools via git, instead of the 1.4.1 source file on
> the ocfs website, and reformatted my partition with the following options
> (just in case)

	Yeah, 1.4.1 tools doesn't know about many of the new features.

> mkfs.ocfs2 -T mail --fs-feature-level=max-features
> --fs-features=backup-super,sparse,unwritten,inline-data,noxattr /dev/sda

	You don't need to specify any of the features here - if mkfs
knows about them, max-features will pull them in.  The only thing on
your fs-features line that isn't covered is noxattr (which turns off
xattr, obviously).

> debugfs.ocfs2 stats now shows:
>         Feature Compat: 3 BackupSuper JBD2SuperBlock
>         Feature Incompat: 2384 Sparse ExtendedSlotMap InlineData MetaECC
> 
> 
> Performance is considerably better when tested with bonnie++ -n
> 25:1024:0:10, probably because of the inline data.

	Inline-data will be the clear winner, yes.  Also, mainline has
some inode allocation changes that help with lots of files.  Don't know
if that affects you.

> Are there any other features im missing that might effect performance?

	We just landed indexed directories in mainline.  Tools support
isn't done yet, though, so you can't enable it without grabbing the
appropriate development code.

> And what does the incompat flags mean?
> I had mistaken them to mean that these features are available but
> incompatible with this partition, ie: not used.

	Nope.  If it's not used on the partition, it's not set.  The
feature set scheme comes from extN.  "Incompat" features are features
that can only be accessed by a filesystem driver that understands them.
So if you load an older ocfs2.ko, and it does not understand an incompat
feature, it will not mount the filesystem.

Joel

-- 

"Nobody loves me,
 Nobody seems to care.
 Troubles and worries, people,
 You know I've had my share."

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127