On Thu, 2011-05-05 at 09:02 -0400, Edward Ned Harvey wrote:
> > From: Garrett D'Amore [mailto:garr...@nexenta.com]
> >
> > We have customers using dedup with lots of vm images... in one extreme
> > case they are getting dedup ratios of over 200:1!
>
> I assume you're talking about a situation where there is an initial VM image,
> and then to clone the machine, the customers copy the VM, correct?
> If that is correct, have you considered ZFS cloning instead?
No. Obviously if you can clone, its better. But sometimes you can't do
this even with v12n, and we have this situation at customer sites today.
(I have always said, zfs clone is far easier, far more proven, and far
more efficient, *if* you can control the "ancestral" relationship to
take advantage of the clone.) For example, one are where cloning can't
help is with patches and updates. In some instances these can get quite
large, and across 1000's of VMs the space required can be considerable.
>
> When I said dedup wasn't good for VM's, what I'm talking about is: If there
> is data inside the VM which is cloned... For example if somebody logs into
> the guest OS and then does a "cp" operation... Then dedup of the host is
> unlikely to be able to recognize that data as cloned data inside the virtual
> disk.
I disagree. I believe that within the VMDKs data is aligned nicely,
since these are disk images.
At any rate, we are seeing real (and large) dedup ratios in the field
when used with v12n. In fact, this is the killer app for dedup.
>
> > Our customers have the ability to access our systems engineers to design the
> > solution for their needs. If you are serious about doing this stuff right,
> > work
> > with someone like Nexenta that can engineer a complete solution instead of
> > trying to figure out which of us on this forum are quacks and which are
> > cracks. :)
>
> Is this a zfs discussion list, or a nexenta sales & promotion list?
My point here was that there is a lot of half baked advice being
given... the idea that you should only use dedup if you have a bunch of
zeros on your disk images is absolutely and totally nuts for example.
It doesn't match real world experience, and it doesn't match the theory
either.
And sometimes real-world experience trumps the theory. I've been shown
on numerous occasions that ideas that I thought were half-baked turned
out to be very effective in the field, and vice versa. (I'm a
developer, not a systems engineer. Fortunately I have a very close
working relationship with a couple of awesome systems engineers.)
Folks come here looking for advice. I think the advice that if you're
contemplating these kinds of solutions, you should get someone with some
real world experience solving these kinds of problems every day, is very
sound advice. Trying to pull out the truths from the myths I see stated
here nearly every day is going to be difficult for the average reader
here, I think.
- Garrett
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
