Bitmaps & Kernel Versions

Bitmaps & Kernel Versions

[Laurent CARON]

Hi,

I'm planning to use bitmaps on some of our RAID1 arrays.

I'm wondering how bitmaps are handeled by older kernels.

Eg: I create a raid array with a bitmap under a 2.6.15 kernel.

I now want to boot under 2.6.12, or even 2.4


Hos is it handeled?
Will it work even if this is my / partition?

Thanks

Laurent

Re: Bitmaps & Kernel Versions

[Neil Brown]

On Wednesday March 15, lcaron@unix-scripts.info wrote:
> Hi,
> 
> I'm planning to use bitmaps on some of our RAID1 arrays.
> 
> I'm wondering how bitmaps are handeled by older kernels.
> 
> Eg: I create a raid array with a bitmap under a 2.6.15 kernel.
> 
> I now want to boot under 2.6.12, or even 2.4
> 
> 
> Hos is it handeled?
> Will it work even if this is my / partition?

On older kernel will not notice the bitmap and will behave
'normally'. 

When you go back to a kernel that understands bitmaps, it will notice
that the bitmap is now out-of-date and will not trust it, but should
start putting fresh data into it.

So it *should* all "just work".  However it hasn't been extensively
tested so I'm not giving any guarantees.

NeilBrown

Re: Bitmaps & Kernel Versions

[Luca Berra]

On Wed, Mar 15, 2006 at 09:08:17PM +1100, Neil Brown wrote:
>On Wednesday March 15, lcaron@unix-scripts.info wrote:
>> Hi,
>> 
>> I'm planning to use bitmaps on some of our RAID1 arrays.
>> 
>> I'm wondering how bitmaps are handeled by older kernels.
>> 
>> Eg: I create a raid array with a bitmap under a 2.6.15 kernel.
>> 
>> I now want to boot under 2.6.12, or even 2.4
>> 
>> 
>> Hos is it handeled?
>> Will it work even if this is my / partition?
>
>On older kernel will not notice the bitmap and will behave
>'normally'. 
>
strange,
last time i tried an older kernel would refuse to activate an md with a
bitmap on it.
I am far from home on a business trip and i don't have kernel-sources at
hand, but i seem to remember that the kernel was very strict on the
feature bitmap in the superblock.

L.

-- 
Luca Berra -- bluca@comedia.it
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Re: Bitmaps & Kernel Versions

[Laurent CARON]

Luca Berra a écrit :
> On Wed, Mar 15, 2006 at 09:08:17PM +1100, Neil Brown wrote:
> 
>> On Wednesday March 15, lcaron@unix-scripts.info wrote:
>>
>>> Hi,
>>>
>>> I'm planning to use bitmaps on some of our RAID1 arrays.
>>>
>>> I'm wondering how bitmaps are handeled by older kernels.
>>>
>>> Eg: I create a raid array with a bitmap under a 2.6.15 kernel.
>>>
>>> I now want to boot under 2.6.12, or even 2.4
>>>
>>>
>>> Hos is it handeled?
>>> Will it work even if this is my / partition?
>>
>>
>> On older kernel will not notice the bitmap and will behave
>> 'normally'.
> 
> strange,
> last time i tried an older kernel would refuse to activate an md with a
> bitmap on it.
> I am far from home on a business trip and i don't have kernel-sources at
> hand, but i seem to remember that the kernel was very strict on the
> feature bitmap in the superblock.
> 
> L.
> 
I experienced the same strange behavior.

Bitmap was created on 2.6.15, tried to boot 2.6.14 and /dev/md0 was not 
started :$.

Strange.....
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