mkfs.xfs ... lazy-count=1 ... not mountable by older kernels?

mkfs.xfs ... lazy-count=1 ... not mountable by older kernels?

[David Sparks]

Hi all,

Is it expected that filesystems made with lazy-count=1 are not mountable by
older kernels?

I'm installing a system based with install media based on 2.6.19 and mkfs.xfs
2.8.11 (its Gentoo 2007.0).  That mkfs.xfs is old so i copied over a 2.9.4
binary and used that to mkfs the filesystem but its unmountable.  Removing the
lazy-count=1 option makes it mountable.

Is this an expected incompatibility or is mix-n-matching xfsprogs a bad idea?

Thanks!

Re: mkfs.xfs ... lazy-count=1 ... not mountable by older kernels?

[David Chinner]

On Tue, Dec 11, 2007 at 11:42:50AM -0800, David Sparks wrote:
> Hi all,
> 
> Is it expected that filesystems made with lazy-count=1 are not mountable by
> older kernels?

That is expected. lazy-count is a mkfs option because it changes the on-disk
format slightly, and older kernels do not understand that format. Hence
mkfs sets a superblock feature bit to prevent the filesystem from being
mounted on kernels that don't understand the slightly different disk format.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group

Re: mkfs.xfs ... lazy-count=1 ... not mountable by older kernels?

[Timothy Shimmin]

David Chinner wrote:
> On Tue, Dec 11, 2007 at 11:42:50AM -0800, David Sparks wrote:
>> Hi all,
>>
>> Is it expected that filesystems made with lazy-count=1 are not mountable by
>> older kernels?
> 
> That is expected. lazy-count is a mkfs option because it changes the on-disk
> format slightly, and older kernels do not understand that format. Hence
> mkfs sets a superblock feature bit to prevent the filesystem from being
> mounted on kernels that don't understand the slightly different disk format.
> 
> Cheers,
> 
> Dave.

And there will be a message in the logs but it probably isn't
overly obvious what it is talking about.

Looking at code, I presume it will come from:
         if (!XFS_SB_GOOD_VERSION(sbp)) {
                 xfs_fs_mount_cmn_err(flags, "bad version");
                 return XFS_ERROR(EWRONGFS);
         }
so there will be a msg about a "bad version".

--Tim

Re: mkfs.xfs ... lazy-count=1 ... not mountable by older kernels?

[Justin Piszcz]

On Wed, 12 Dec 2007, Timothy Shimmin wrote:

> David Chinner wrote:
>> On Tue, Dec 11, 2007 at 11:42:50AM -0800, David Sparks wrote:
>>> Hi all,
>>> 
>>> Is it expected that filesystems made with lazy-count=1 are not mountable 
>>> by
>>> older kernels?
>> 
>> That is expected. lazy-count is a mkfs option because it changes the 
>> on-disk
>> format slightly, and older kernels do not understand that format. Hence
>> mkfs sets a superblock feature bit to prevent the filesystem from being
>> mounted on kernels that don't understand the slightly different disk 
>> format.
>> 
>> Cheers,
>> 
>> Dave.
>
> And there will be a message in the logs but it probably isn't
> overly obvious what it is talking about.
>
> Looking at code, I presume it will come from:
>        if (!XFS_SB_GOOD_VERSION(sbp)) {
>                xfs_fs_mount_cmn_err(flags, "bad version");
>                return XFS_ERROR(EWRONGFS);
>        }
> so there will be a msg about a "bad version".
>
> --Tim
>
>

Has anyone done any benchmarks with Dave Chinner's recommendations for 
mkfs.xfs/optmizations?

Justin.