ATA over Ethernet (aoe) Experience?

["Kent Borg" <user=107@nabble.blu.org>]

 Anyone here have experience with ATA over Ethernet ("aoe")? 

To be specific, here is my idea: I want to do more of that trendy 
"server consolidation" but not have all my eggs in one basket.  So I 
imagine having two identical physical machines, each set up to match the 
other.  Normally I run all the VMs on one machine.  Worrying about disks 
dying I put each VM on a pair of software raid 1 disks in that box.  But 
how do I quickly switch to the other physical machine? 

Here is where I get clever (and ask for advice):  On the other machine I 
do the exact same thing.  VM on a pair of software raid 1 partitions. 
But how to sync them up? 

First, shut down the spare copy.  Only run one copy of the VM at a time. 

Second, shutdown the md device for that spare copy. 

Third, export the two physical partions via ATA over ethernet.  (Be an 
aoe target.) 

Fourth, on the primary machine, import the two partitions via ATA over 
ethernet.  (Be an aoe initiator.) 

Fifth, on the primary machine, add the two partitions to the raid 1 md 
device.  Wait for the data to copy, but still keep the VM running and 
serving whatever good stuff it does. 


I haven't researched it much, but if I have dedicated gigabit ethernet 
)or faster) and a crossover cable, and do a large MTU hack on those two 
NICs, maybe the ATA over ethernet could mostly keep up with the local 
disks?  Or maybe not... 

Next obvious idea would be to not ship both partitions over the ethernet 
cable separately, but to put them together into a raid 1 pair first and 
instead ship the md device over the cable. 

But there is something else I would like to do: run the VM on one 
physical machine, shut it down, reverse the ATA over ethernet setup, 
boot the VM on the other physical machine, and have the various md 
components all happy and in synch with no replication necessary.  Doing 
a flat collection of 4 distinct physical partitions would probably 
work.  But if I did nested and rehanging the tree, a complete 
replication would have to happen unless I did some hacking. 

Example. 

case 1: 
  - yin's sda1 
  - yin's sdb1 
  - yang's aoe, which is 
    - yang's sda1 
    - yang's sdb1 

case 2: 
  - yang's sda1 
  - yang's sdb1 
  - yin's aoe, which is 
    - yin's sda1 
    - yin's sdb2 

Is there a way to hack md internals to make the two cases boot back and 
forth and keep the md in synch both ways? 


Practical consession: maybe just running in this aoe mode while messing 
with configurations and migrating VMs, and just run local raid 1 when 
things are stable. 


Comments? 


Thanks, 

-kb 

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