[dm-devel] mirroring: [patch 1 of 8] device failure tolerance

[Jonathan E Brassow]

On Jun 30, 2005, at 11:38 AM, Greg Freemyer wrote:

> On 6/30/05, Jonathan E Brassow <jbrassow at redhat.com> wrote:
>>
>> On Jun 30, 2005, at 10:13 AM, Greg Freemyer wrote:
>>
>>> On 6/29/05, Jonathan E Brassow <jbrassow at redhat.com> wrote:
>>>> This patch defines a couple more states that logs can return, and
>>>> checks for those states in the mirror code.  The states are useful 
>>>> for
>>>> logs that have cluster support.
>>>>
>>>>   brassow
>>>
>>> Have I been asleep?  This is the first I heard of DM having cluster
>>> mirror support.  I assume the goal is something along the lines of
>>> what DRBD provides.
>>>
>>> Can someone give a very high-level overview of current status, plans,
>>> etc. related to DM Cluster Mirror support.  And if this related to 
>>> the
>>> DRBD project?
>>
>> Please note that the "mirroring [patch x of 8]..." set for device 
>> fault
>> tolerance has been replaced with the "mirroring [patch x of 6]..." 
>> set.
>>
>> The cluster mirroring that I'm talking about is active/active and
>> capable of handling more than 2 nodes.  It would be used in 
>> conjunction
>> with a clustered file system - like GFS.  The application sitting on
>> the cluster mirror should be cluster-aware.  You wouldn't be able to
>> just put ext3 on there and expect it to work in a cluster capacity.
>>
>> Although there are some minor things that need to happen in the mirror
>> proper code (as can be seen from the smallness of the cluster patch),
>> the heavy lifting is done by a cluster-aware log.  That is were you 
>> are
>> keeping track of clean/dirty/recovering state.
>>
>> An out-dated (but still useful for background) dock can be found at
>> http://www.brassow.com/mirroring/index.html
>>
>>   brassow
>>
>
> Sounds like you have more ambitious plans than DRBD.   (They have
> active-passive now and IIRC they plan the next major release to have
> active-active, but I think only on 2 nodes.)
>
> Is the GFS team planning on supporting this infrastructure.  I hope so.
>

Yes.  In fact, the cluster log being developed leverages the Red hat 
cluster manager (cman) - the same one that GFS uses.

CMAN is moving to user space (I think in the FC5 timeframe?), so the 
cluster log will have to adapt to that.  I won't be submitting the 
cluster log code until that takes place.  It is available in the 
cluster repository though (sources.redhat.com/cluster), but i will have 
to clean it up again to take advantage of the hooks I added to the 
logging code.

  brassow