Re: [PATCH] md: forbid a RAID5 from having both a bitmap and a journal.

[Wols Lists <antlists@youngman.org.uk>]

On 18/10/17 02:51, Joshua Kinard wrote:
> On 10/17/2017 17:03, NeilBrown wrote:
>> On Tue, Oct 17 2017, John Stoffel wrote:
>>
>>>>>>>> "NeilBrown" == NeilBrown  <neilb@suse.com> writes:
>>>
>>> NeilBrown> Having both a bitmap and a journal is pointless.
>>> NeilBrown> Attempting to do so can corrupt the bitmap if the journal
>>> NeilBrown> replay happens before the bitmap is initialized.
>>> NeilBrown> Rather than try to avoid this corruption, simply
>>> NeilBrown> refuse to allow arrays with both a bitmap and a journal.
>>> NeilBrown> So:
>>> NeilBrown>  - if raid5_run sees both are present, fail.
>>>
>>> So what happens if there's someone out there with an array setup with
>>> both already?  Should the journal or the bitmap be removed at this
>>> time?  
>>
>> If someone has an array like that they can assemble it with
>>   --update=no-bitmap
> 
> IMHO, this should probably get documented in the Linux RAID Wiki once it goes
> through.
> 
Done! I'm not sure where it should go, so under "When things go wrogn",
I've put it in the "easy fixes" section. It simply notes that you are
now not allowed to combine journals and bitmaps, and gives the fix. (It
also says when "now" is :-)
> 
>> I'd rather not automatically disable things.
>>
Cheers,
Wol