Re: [Xen-users] HA Xen on 2 servers!! No NFS, special hardware, DRBD or iSCSI...

[Chris de Vidal <chris@xxxxxxxxxx>]

--- Chris de Vidal <chris@xxxxxxxxxx> wrote:
> If you don't mind patching your DomU kernel (I prefer not to) with the fast 
> sync patch, this
> might actually work.

Excuse me, it's called "Fast RAID 1" or fr1 and it's found here:
ftp://oboe.it.uc3m.es/pub/Programs/
It is "intelligent" in that it doesn't blindly resynchronize a whole mirror 
component when only a
few blocks need resyncing.  That can save hours of resync time on a large 
device. In addition, it
always chooses the fastest device to read from on reads.


Exactly what we're looking for!  Does not require NBD, from what I can tell...


Reflecting upon this some more, I think perhaps it could be done in Dom0, 
making setting up
software RAID inside the DomUs unnecessary.  But that requires a shared 
hardware-like setup.  DRBD
0.7 doesn't allow primary/primary (equivalent to shared hardware) but things 
like AoE do (NBD
should, too).  When DRBD 0.8 becomes more stable and primary/primary is 
possible, perhaps that
will be an option.  I like the DRBD project and would be eager to try it.

As Eric said, using AoE means any network interruption generates a resync.  But 
then that's a
concern with /ANY/ AoE or iSCSI + software RAID setup.  So methinks AoE isn't 
too bad.  Add in the
fr1 patch and it might be usable.

If one were to patch the kernel with the "Fast RAID" patch and use AoE to 
create /dev/md0 on Dom0
using both a local disk and a remote, this might work!  In this case, LVM would 
no longer be a
necessity.


Does anyone know if Xen's live migration requires something like GFS on shared 
hardware?  Or does
it take care of the problem as long as it's the only thing accessing the drive?

CD

TenThousandDollarOffer.com

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