Re: [RFC][PATCH 0/4] dm-log: support multi-log devices

[Takahiro Yasui <tyasui@redhat.com>]

Hi Malahal,

malahal@us.ibm.com wrote:
> Takahiro Yasui [tyasui@redhat.com] wrote:
>> In addition, the multi-log feature is efficient and very important
>> at system booting. It is highly possible that disks get broken.
>> I think that the current log feature can not save this situation
>> because there is only one log disk and there is only way to construct
>> a mirror by "core" log. Then, a whole disk replication will be triggered.
>>
>> Do you have a good idea to save it, too? If there is, it could be
>> an another solution of our concern.
> 
> A while back IBM posted a patch to LVM that constructs a log device with
> a mirror and then creates the real mirror using such a mirrored log
> device. I think this may solve your problem. It was completely written
> in LVM and Stefan refreshed it to the latest LVM.

Thank you for the comment and information. It seems that your
approach seems to address my problem, too. Here I have a concern
about write performance because an additional mirror mapping might
introduce additional delay and overhead. In addition, error for
log devices is better to be handled by the simple way, and a basic
error handling would work.

I couldn't find any discussion after you posted the patch.
Could you tell me if IBM also have the same background as I have,
or do you have another issue to solve? I would also like to know
if my approach solves your problem.

> Anyone thinks this user level only solution is any better? We will be
> very happy to have any one of the solutions in upstream!

Yes, I appreciate many comments and I'm glad to have a solution
in upstream, too.

> Here is a link the posted patch
> (http://permalink.gmane.org/gmane.linux.kernel.device-mapper.devel/3988)
> 
> 
> --Malahal.