[Dovecot] Best Cluster Storage

[Brad Davidson]

> -----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