On 15/01/11 01:14, Brad Davidson wrote:
-----Original Message-----
I'm sorry I don't follow this. It would be appreciated if you could
include a simpler example. The way I see it, a VM disk is just a
small
chunck "LVM LV in my case" of a real disk.
Perhaps if you were to compare and contrast a virtual disk to a raw
disk, that would help. If you wanted to use drbd with a raw disk being
accessed via a VM guest, that would probably be all right. Might not
be
"supported" though.
Depending on your virtualization method, raw device passthrough would
probably be OK. Otherwise, think about what you're doing - putting a
filesystem - on a replicated block device - that's presented through a
virtualization layer - that's on a filesystem - that's on a block
device. If you're running GFS/GlusterFS/etc on the DRBD disk, and the VM
is on VMFS, then you're actually using two clustered filesystems!
Each layer adds a bit of overhead, and each block-on-filesystem layering
adds the potential for block misalignments and other issues that will
affect your overall performance and throughput. It's just hard to do
right.
-Brad
Generally, I would give an LVM LV to each of my Xen guests, which
according to the DRBD site, is ok:
http://www.drbd.org/users-guide/s-lvm-lv-as-drbd-backing-dev.html
I do not use img files with loopback devices
Is this a bit better now?
