Les Mikesell <lesmikesell AT gmail DOT com> wrote on 09/11/2009 12:14:22 PM:

> Timothy J Massey wrote:
> > 
> > So you're attempting to convert a physical BackupPC server into a 
virtual 
> > image?  VMware has conversion tools that do this.  I've only used the 
> > Windows version of VMware Converter, but it has worked perfectly for 
> > converting a physical host into a virtual host.  There is a Linux 
version.
> 
> I'm hoping to accomplish a couple of different things in one step.  I 
> don't want to convert my existing server to VMware.  I want to make a 
> snapshot copy of the backuppc partition with as little downtime as 
> possible - and sync'ing a RAID member will do that.  Then I want a copy 
> of that offsite - and so far splitting into 2GB chunks looks like a good 

> way to make rsync work.  Then, if the chunked remote copy just happened 
> to be in a form that could connect up directly to a VMware guest that 
> could be set up for disaster recover restores, so much the better.

Sure.  I can see that you want to do that.  But I think you're trying to 
shoehorn too much into a single process--and requiring pieces (i.e. VMDK) 
that weren't designed to do what you're asking of them.  I think you're 
wanting more than the tools will deliver.

But go for it--prove me wrong!  :)

> > And if all you're doing is to try to capture a file-based version of 
your 
> > block device (a physical partition) that you want to mount using some 
> > other physical server (or even a virtual server, come to think of it), 
I 
> > think you'd be *far* better off just dd'ing the partition into a file 
and 
> > using a loopback mount to mount it someplace else.
> > 
> > In other words, the only time you should be dealing with VMDK files is 
if 
> > you're trying to create a new virtual guest.  And if you are doing 
this, 
> > the proper way of doing this is *not* by trying to use LVM/RAID 
weirdness, 
> > but using the VMware Converter tools to do this for you properly.
> > 
> > If you're *not* trying to create a new virtual guest, then don't mess 
with 
> > VMDK files.  They're an annoyance that should only be dealt with if 
you 
> > actually have to.
> 
> I'd like to accomplish both at once - that is, image copy/raid sync to 
> get a snapshot, and have the result usable by a separate VM.  However, I 

> haven't been able to figure out how do do it with the vmware (server 
> 2.x) utilities.  I can create a chunked disk with vmware-diskmanager and 

> I can connect it so the host sees the whole disk image in one piece with 

> vmware-mount and the -f option, but I can't find a way to see a raw 
> partition.  I could mount a single partition if it had a filesystem on 
> it but I don't see how to access the partition in a way that mdadm will 
> like.

Like I said, you may want to do it, but wanting it won't make it so, 
unfortunately.

> > VirtualBox compares fairly with the free VMware Server, but VMware 
server 
> > is about 10% of what you can do with VMware--with the paid-for tools.
> > 
> > When it comes to commercial tools, VMware is in a class by itself, 
though 
> > Citrix is trying hard with XenServer (still too cumbersome and 
unpolished 
> > compared to VMware, and requires VM hardware for Windows).  When it 
comes 
> > to free-as-in-beer, XenServer is the best.  It's still cumbersome, but 

> > they give you several of the items for free that VMware charges for.
> > 
> > VirtualBox is neither the best tool overall, nor the best tool for 
free. 
> > And unfortunately, the GPL'ed code is only a fraction of what you 
really 
> > need for a usable virtualization environment.  If you want GPL tools, 
KVM 
> > (especially in RHEL 5.4) is the best around.
> 
> I'm not convinced that any of that matters when the real issue is moving 

> a physical disk head around.

If that's all you want out of life, then pick whatever.  For most people, 
vMotion is a killer app.  The only reason I would use a solution that 
*doesn't* provide this would be 100% GPL--which is why I'm keeping a very 
close eye on KVM.

> > How much performance do you lose using a loopback mount?  It's *gotta* 
be 
> > less than the overhead of virtualization!  I like that idea even 
better. 
> 
> This is the effect I was hoping to get by vmware-mounting the vmdk into 
> the physical host.

And I think you'd be a million times better by just using a simple 
loopback mount--which could be used by a physical *or* a virtual host with 
zero drawbacks, outside of loopback itself.  And it's rsyncable.

I go back to my original statement:  unless you're *trying* to migrate 
something to a virtual guest, don't saddle yourself with VMDK's.  We use 
them because we have to, not because we *want* to.  Use the loopback.  You 
still haven't given me a drawback for this, other than "I want to use 
VMDK's, even though they aren't designed to be generic containers for 
data."  VMDK files are not tar files, here...

Again, a virtual guest can use a loopback file *just* as easily as a 
physical host...

> Maybe the fuse/perl driver mentioned earlier would work with one end in 
> the physical backuppc server and the other in the remote disaster 
> recovery VMware guest.   But, there is a timing issue unless some sort 
> of local snapshot capability is added and I'd prefer to avoid LVM.  I 
> suppose I could sync my existing disk into the raid, break it, and mount 

> it back separately for the rsync step to decouple the transfer time.

You have *way* too many preconditions.

"I want to deal with my partitions as files"

 -- Then use loopback

"But I want to use VMDK files"

 -- Then use the VMware Converter Tools

"But I only want to do *some* partitions"

 -- Then use LVM and snapshot them

"But I don't want to use LVM"

 -- Well, then, I guess you're out of luck...

http://en.wikipedia.org/wiki/Moving_the_goalpost

Tim Massey


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