Bigendian issue with mdadm

Bigendian issue with mdadm

[Francois Barre]

Hi All,

Please, Help !

I've created a raid5 array on a x86 platform, and now wish to use it
on a mac mini (g4 based). But the problem is : the first is
little-endian, the second big-endian...
And it seams like md superblock disk format is hostendian, so how
should I say mdadm to use a endianness ?

Thanks for help,

F.-E.B.

Re: Bigendian issue with mdadm

[Neil Brown]

On Monday February 20, francois.barre@gmail.com wrote:
> Hi All,
> 
> Please, Help !
> 
> I've created a raid5 array on a x86 platform, and now wish to use it
> on a mac mini (g4 based). But the problem is : the first is
> little-endian, the second big-endian...
> And it seams like md superblock disk format is hostendian, so how
> should I say mdadm to use a endianness ?
> 

Read the man page several times?

Look for "--update=byteorder"

You need mdadm-2.0 or later.

NeilBrown

Re: Bigendian issue with mdadm

[Luca Berra]

On Tue, Feb 21, 2006 at 10:44:22AM +1100, Neil Brown wrote:
>On Monday February 20, francois.barre@gmail.com wrote:
>> Hi All,
>> 
>> Please, Help !
>> 
>> I've created a raid5 array on a x86 platform, and now wish to use it
>> on a mac mini (g4 based). But the problem is : the first is
>> little-endian, the second big-endian...
>> And it seams like md superblock disk format is hostendian, so how
>> should I say mdadm to use a endianness ?
>> 
>
>Read the man page several times?
>
>Look for "--update=byteorder"
>
>You need mdadm-2.0 or later.
>
besides IIRC version 1 super block is always little-endan.

L.

-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
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Re: Bigendian issue with mdadm

[Neil Brown]

On Tuesday February 21, bluca@comedia.it wrote:
> On Tue, Feb 21, 2006 at 10:44:22AM +1100, Neil Brown wrote:
> >On Monday February 20, francois.barre@gmail.com wrote:
> >> Hi All,
> >> 
> >> Please, Help !
> >> 
> >> I've created a raid5 array on a x86 platform, and now wish to use it
> >> on a mac mini (g4 based). But the problem is : the first is
> >> little-endian, the second big-endian...
> >> And it seams like md superblock disk format is hostendian, so how
> >> should I say mdadm to use a endianness ?
> >> 
> >
> >Read the man page several times?
> >
> >Look for "--update=byteorder"
> >
> >You need mdadm-2.0 or later.
> >
> besides IIRC version 1 super block is always little-endan.
> 

True.  v1 is little-endian, not host-endian so this issue won't appear
if using v1 metadata.  However the default is 0.90, and I'm still
finding occasional bugs with the v1 code, so I'm not likely to change
the default soon any time soon... probably not for 1 year after I'm as
confident of v1 code as of v0.90.

NeilBrown

Re: Bigendian issue with mdadm

[Francois Barre]

2006/2/21, Neil Brown <neilb@suse.de>:
> On Monday February 20, francois.barre@gmail.com wrote:
> > Hi All,
> >
> > Please, Help !
> >
[...]
> > And it seams like md superblock disk format is hostendian, so how
> > should I say mdadm to use a endianness ?
> >
>
> Read the man page several times?
>
> Look for "--update=byteorder"
>
> You need mdadm-2.0 or later.
>
> NeilBrown
>

Ooops... You know what it is : the more you focus on a problem, the
less you can see solutions floating around...
I had mdadm-1.2 installed, and of course did not think about
upgrading... I will test this asap.
This will avoid me to code a byte reordering program... Thanks Neil !
BTW : I did not see this feature in the kernel code, and after a quick
look at mdadm source, seems to be implemented in
super0.c:super0_swap_endian(). Is there any prerequisite regarding the
kernel version for this to work ?

Thanks again Neil, I am really impressed by your patience answering
dummy questions...

Regards,