Yesterday Maish and Christian had a nice little back and forth on their blogs about VSAN. Maish published a post titled “VSAN – The Unspoken Truth” which basically talks about how VSAN doesn’t fit blade environments, and how many enterprise environments adopted blade to get better density from a physical point of view. With that meaning increase the number of physical servers to the number of rack U(nits) consumed. Also there is the centralized management aspect of many of these blade solutions that is a major consideration according to Maish.
Christian countered this with a great article titled “VSAN – The Unspoken Future“. I very much agree with Christian’s vision. Christian’s point basically is that when virtualization was introduced IT started moving to blade infrastructures as that was a good fit for the environment they needed to build. Christian then explains how you can leverage for instance the SuperMicro Twin architecture to get a similar (high physical) density while using VSAN at the same time. (See my Twin posts here) However, the essence of the article is: “it shows us that Software Designed Data Center (SDDC) is not just about the software, it’s about how we think, manage AND design our back-end infrastructure.”
There are three aspects here in my opinion:
- Density – the old physical servers vs rack units discussion.
- Cost – investment in new equipment and (potential) licensing impact.
- Operations – how do you manage your environment, will this change?
First of all, I would like to kill the whole density discussion. Do we really care how many physical servers you can fit in a rack? Do we really care you can fit 8 or maybe even 16 blades in 8U? Especially when you take in to consideration your storage system sitting next to it takes up another full rack. Than on top of that there is the impact density has in terms of power and cooling (hot spots). I mean if I can run 500 VMs on those 8 or 16 blades and that 20U storage system, is that better or worse than 500 VMs on 12 x 1U rack mounted with VSAN? I guess the answer to that one is simple: it depends… It all boils down the total cost of ownership and the return on investment. So lets stop looking at a simple metric like physical density as it doesn’t say much!
Before I forget… How often have we had those “eggs in a basket” discussions in the last two years? This was a huge debate 5 years back, in 2008/2009 did you really want to run 20 virtual machines on a physical host? What if that host failed? Those discussions are not as prevalent any longer for a good reason. Hardware improved, stability of the platforms increased, admins became more skilled and less mistakes are made… chances of hitting failures simply declined. Kind of like the old Microsoft blue screen of death joke, people probably still make the joke today but ask yourself how often does it happen?
Of course there is the cost impact. As Christian indicated, you may need to invest in new equipment… As people mentioned on twitter: so did we when we moved to a virtualized environment. And I would like to add: and we all know what that brought us. Yes there is a cost involved. The question is how do you balance this cost. Does it make sense to use a blade system even for VSAN when you can only have a couple of disks at this point in time? It means you need a lot of hosts, and also a lot of VSAN licenses (+maintenance costs). It may be smarter, from economical point of view, to invest in new equipment. Especially when you factor in operations…
Operations, indeed… what does it take / cost today to manage your environment “end to end”? Do you need specialized storage experts to operate your environment? Do you need to hire storage consultants to add more capacity? What about when things go bad, can you troubleshoot the environment by yourself? How about my compute layer, most blade environments offer centralized management for those 8 or 16 hosts. But can I reduce the number of physical hosts from 16 or 8 to for instance 5 with a slightly larger form factor? What would the management overhead be, if there is any? Each of these things need to be taken in to considerations and somehow quantified to compare.
Reality is that VSAN (and all other hyper-converged solutions) brings something new to the table, just like virtualization did years ago. These (hyper-converged) solutions are changing the way the game is played, so you better revise your play book!