VFS ROADMAP (and vfs01.patch stage 1 available for testing)

Jeroen Ruigrok/asmodai asmodai at wxs.nl
Mon Aug 16 22:47:53 PDT 2004

-On [20040817 07:32], Matthew Dillon (dillon at xxxxxxxxxxxxxxxxxxxx) wrote:
>    This is a question with a very, very complex answer.  If I were to
>    try to simplify it and put it in layman's terms, we will almost 
>    certainly have to use the resource accessibility model.  So what
>    happens would depend on what was running on the node that went down
>    and whether the resources are recoverable or not.  Processes beholden
>    to the dead node or needing critical resources (like memory) on the dead
>    node would probably be killed by default.

Most high availability clusters have proprietary memory interlinks for this
end.  Wasn't there some development/work on sharing memory state over
(dedicated) Ethernet links?

Otherwise you might need to work with process checkpointing and migrating
those states to centralised controller boxes every once in a while to not
loose work.  But then you need to make sure you can safely migrate process
to other boxes anyway.
One big hurdle is: overcoming different hardware configurations.

>    Recoverable resources, such as a block device representing a physical
>    disk, could result in dependant proceses blocking until the resource
>    becomes available again.  If the block device is part of a RAID then
>    theoretically dependant processes would still be able to run as long as
>    the RAID as a whole remains intact.

I think with hardware RAID we should not need to worry about that.  And
software RAID is also a separate subsystem.
The blocked issue reminds me of NFS shares just going away and leaving a box
wedged until it gets back online. :S

Most clusters I've seen also typically work with quorum disks.

Jeroen Ruigrok van der Werven <asmodai(at)wxs.nl> / asmodai / kita no mono
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