Re: linux raid wiki - backup files

[Anthony Youngman <antlists@youngman.org.uk>]

On 21/11/16 14:07, Phil Turmel wrote:
> On 11/20/2016 09:48 AM, Wols Lists wrote:
>> On 20/11/16 00:27, Phil Turmel wrote:
>>> Yes.  But the new stripes lay on top of the old stripes, unless you move
>>> the data offset.  Which is why a backup file holds the old stripe just
>>> in case.  If you can move the offset, you use the lower offset for the
>>> lower addresses in the array, and the higher offset for the higher
>>> addresses, on either side of the reshape position.
>>
>> Okay, understood. So v0.9 and v1.0 always need a backup for a reshape.

Having looked at the man page, this now seems obvious - the superblock 
is at the end, so the data offset is 0. But for a 1.0 array, could we 
create a data offset?

(So, if we created a data offset, we could then move the superblock and 
convert a 1.0 to 1.1 or 1.2? Okay, it can't do it now, but it looks to 
me like it shouldn't be that hard ... ?)
>>
>> But if we have a data offset with v1.2, a reshape will use that space if
>> it can rather than needing a backup file?
>
I'm guessing that 1.0 and 1.1 defaulted to no data offset to speak of? 
And if we (can) create a decent data offset, we can then use that in 
exactly the same way as with v1.2?

Cheers,
Wol