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

[Takahiro Yasui]

malahal at us.ibm.com wrote:
> Takahiro Yasui [tyasui at redhat.com] wrote:
>>> Not really. What I meant is re-integrating a failed log device when it
>>> comes back again. That is also what I mean by handling 'transient
>>> errors'.
>> Thanks, I see your requirement on this feature.
>> Let me put one more question.
>>
>> LVM mirroring is used to make system available even if some devices,
>> such as data and log device, have a problem. Currently, activations
>> by "vgchange -ay" command seem to fail during system booting if one
>> of devices related to VG are missing or had I/O error. For example,
>> if a mirror is structured by two data devices and log devices, the
>> mirror logical device should be activated and used even if one data
>> device and one log device are missing.
>>
>> Could you give me an idea or solution to handle this? Do we need to
>> enhance your feature to achieve this requirement?
> 
> The requirement you are asking is more than "mirrored log" support.
> Actually it is nothing to do with "mirrored log" support! LVM has
> "--partial' option but that creates read-only volumes.  IBM has
> implemented "--partial-rw" that activates such mirror devices.
> Essentially it creates an 'error device' in place of a missing device,
> but the patch isn't complete as it doesn't work well with other segment
> (target) types!
> 
> What we need is changes to LVM "--partial" code path where it can create
> volumes read-only or read-write based on what is available instead of
> blindly doing read-only.

Thank you for the kind reply. I tried the latest lvm command as
Alasdair suggested, and it seems to work as I expected.

I will test the latest lvm command first.

Thanks,
Taka