Re: [Xen-users] Re: Re: Redundant server setup

[Javier Guerra <javier@xxxxxxxxxxx>]

On Friday 12 May 2006 8:31 am, Matthew Wild wrote:
> But as far as I can see, DRBD only provides twin machine shared storage. I
> have a few servers I want to use as dom0s and since they are generally
> simple 1U boxes I want them as clean from local storage as possible. The

this is a setup i'd be willing to use:
(of course, if money isn't an issue, i'd buy some big iron storage from EMC or 
such)

1) a box with two GigE and big SATA disks, (there's a nice supermicro 3U box 
with 15 bays, i'd do two 7-disk RAID5 plus one hotspare).  Call it S1A, and 
the two volumes S1A1 and S1A2.
2) build another one identical to S1A, call it S1B, with volumes S1B1 and S1B2
3) use a crossover cable on eth1 of S1A and S1B.  run DRBD on both boxes to 
join S1A1 with S1B1 and S1A2 with S1B2
4) on each box, export the replicated volumes on eth0 with GNBD, iSCSI or AoE
5) call the whole group S1.  there are two volumes: S1.1 and S1.2; each have 
two 'paths': S1A1 and S1B1 to S1.1 , and S1A2 and S1B2 to S1.2

6) add new pairs S2, S3, etc

7) on the Xen boxes, configure dom0 to access all shared volumes, but using 
only one path for each volumen.  e.g. on the first Xen box, reach S1.1 via 
S1A1, S1.2 via S1B2, S2.1 via S2A1 and S2.2 via S2B2.  try to balance how 
many Xen boxes use the 'A' path for a volume, and how many use the 'B' path 
for the same volume.

8) setup a cluster aware Volume manager on all dom0s; either CLVM or EVMS with 
HA
9) create one single big volume group with all the shared volumes.
10) split the volume group on several logical volumes, 'feed' these to the 
domUs

one further thing i've just thought, it would be possible to put all 'A' 
member of each storage pair on a switch, and all 'B' members on another.  the 
Xen boxes would have to have two ethernet ports each, one to the 'real' LAN, 
and the other to the storage LAN, half on the A side, half on the B side.  
now not even the storage LAN is a failure point, but all Xen boxes can see 
all volumes and do live migration from any box to any other, no matter if 
they use the same or different storage switch.

Again, if i had so much money to spend, i'd probably just call EMC, IBM, or 
someone else to build it for me with FC (or Infiniband? i can hope..)

-- 
Javier

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