Category Archives: Matrix

Is Your Blade Ready for Virtualization? A Math Lesson.

I attended the second day of the HP Converged Infrastructure Roadshow in NYC last week. Most of the day was spent watching PowerPoints and demos for the HP Matrix stuff and Virtual Connect. Then came lunch. I finished my appetizer and realized that the buffet being set up was for someone else. My appetizer was actually lunch! Thanks God there was cheesecake on the way…

There was a session on unified storage, which mostly covered the LeftHand line. At one point, I asked if the data de-dupe was source based or destination based. The “engineer” looked like a deer in the headlights and promptly answered “It’s hash based.” ‘Nuff said… The session covering the G6 servers was OK, but “been there done that.”

Other than the cheesecake, the best part of the day was the final presentation. The last session covered the differences in the various blade servers from several manufacturers. Even though I work for a company that sells HP, EMC and Cisco gear, I believe that x64 servers, from a hardware perspective, are really generic for the most part. Many will argue why their choice is the best, but most people choose a brand based on relationships with their supplier, the manufacturer or the dreaded “preferred vendor” status.  Obviously, this was an HP – biased presentation, but some of the math the Bladesystem engineer (I forgot to get his name) presented really makes you think.

Lets start with a typical configuration for VMs. He mentioned that this was a “Gartner recommended” configuration for VMs, but I could not find anything about this anywhere on line. Even so, its a pretty fair portrayal of a typical VM.

Typical Virtual Machine Configuration:

  • 3-4 GB Memory
  • 300 Mbps I/O
    • 100 Mbps Ethernet (0.1Gb)
    • 200 Mbps Storage (0.2Gb)

Processor count was not discussed, but you will see that may not be a big deal since most processors are overpowered for todays applications (I said MOST). IOps is not a factor either in these comparisons, that would be a factor of the storage system.

So, let’s take a look at the typical server configuration. In this article, we are comparing blade servers. But this is even typical for a “2U” rack server. He called this an “eightieth percentile” server, meaning it will meet 80% of the requirements for a server.

Typical Server Configuration:

  • 2 Sockets
    • 4-6 cores per socket
  • 12 DIMM slots
  • 2 Hot-plug Drives
  • 2 Lan on Motherboard (LOM)
  • 2 Mezzanine Slots (Or PCI-e slots)

Now, say we take this typical server and load it with 4GB or 8GB DIMMs. This is not a real stretch of the imagination. It gives us 48GB of RAM. Now its time for some math:

Calculations for a server with 4GB DIMMs:

  • 48GB Total RAM ÷ 3GB Memory per VM = 16 VMs
  • 16 VMs ÷ 8 cores = 2 VMs per core
  • 16 VMs * 0.3Gb per VM = 4.8 Gb I/O needed (x2 for redundancy)
  • 16 VMs * 0.1Gb per VM = 1.6Gb Ethernet needed (x2 for redundancy)
  • 16 VMs * 0.2Gb per VM = 3.2Gb Storage needed (x2 for redundancy)

Calculations for a server with 8GB DIMMs:

  • 96GB Total RAM ÷ 3GB Memory per VM = 32 VMs
  • 32 VMs ÷ 8 cores = 4 VMs per core
  • 32 VMs * 0.3Gb per VM = 9.6Gb Ethernet needed (x2 for redundancy)
  • 32 VMs * 0.1Gb per VM = 3.2Gb Ethernet needed (x2 for redundancy)
  • 32 VMs * 0.2Gb per VM = 6.4Gb Storage needed (x2 for redundancy)

Are you with me so far? I see nothing wrong with any of these yet.

Now, we need to look at the different attributes of the blades:


* The IBM LS42 and HP BL490c Each have 2 internal non-hot plug drive slots

The “dings” against each:

  • Cisco B200M1 has no LOM and only 1 mezzanine slot
  • Cisco B250M1 has no LOM
  • Cisco chassis only has one pair of I/O modules
  • Cisco chassis only has four power supplies – may cause issues using 3-phase power
  • Dell M710 and M905 have only 1GbE LOMs (Allegedly, the chassis midplane connecting the LOMs cannot support 10GbE because they lack a “back drill.”)
  • IBM LS42 has only 1GbE LOMs
  • IBM chassis only has four power supplies – may cause issues using 3-phase power

Now, from here, the engineer made comparisons based on loading each blade with 4GB or 8GB DIMMs. Basically, some of the blades would not support a full complement of VMs based on a full load of DIMMS. What does this mean? Don’t rush out and buy blades loaded with DIMMs or your memory utilization could be lower than expected. What it really means is that you need to ASSESS your needs and DESIGN an infrastructure based on those needs. What I will do is give you a maximum VMs per blade and per chassis. It seems to me that it would make more sense to consider this in the design stage so that you can come up with some TCO numbers based on vendors. So, we will take a look at the maximum number of VMs for each blade based on total RAM capability and total I/O capability. The lower number becomes the total possible VMs per blade based on overall configuration. What I did here to simplify things was take the total possible RAM and subtract 6GB for hypervisor and overhead, then divide by 3 to come up with the amount of 3GB VMs I could host. I also took the size specs for each chassis and calulated the maximum possible chassis per rack and then calculated the number of VMs per rack. The number of chassis per rack does not account for top of rack switches. If these are needed, you may lose one chassis per rack most of the systems will allow for an end of row or core switching configuration.

Blade Calculations

One thing to remember is this is a quick calculation. It estimates the amount of RAM required for overhead and the hypervisor to be 6GB. It is by no means based on any calculations coming from a real assessment. The reason why the Cisco B250M1 blade is capped at 66 VMs is because of the amount of I/O it is capable of supporting. 20Gb redundant I/O ÷ 0.3 I/O per VM = 66 VMs.

I set out in this journey with the purpose of taking the ideas from an HP engineer and attempted as best as I could to be fair in my version of this presentation. I did not even know what the outcome would be, but I am pleased to find that HP blades offer the highest VM per rack numbers.

The final part of the HP presentation dealt with cooling and power comparisons. One thing that I was surprised to hear, but have not confirmed, is that the Cisco blades want to draw more air (in CFM) than one perforated tile will allow. I will not even get into the “CFM pre VM” or “Watt per VM” numbers, but they also favored HP blades.

Please, by all means challenge my numbers. But back them up with numbers yourself.

Cisco B200M1 Cisco B250M1 Dell M710 Dell M905 IBM LS42 HP BL460c HP BL490c HP BL685c
Max RAM 4GB DIMMs 48 192 72 96 64 48 72 128
Total VMs Possible 16 64 24 32 21 16 24 42
Max RAM 8GB DIMMs 96 384 144 192 128 96 144 256
Total VMs Possible 32 128 48 64 42 32 48 85
Max Total Redundant I/O 10 20 22 22 22 30 30 60
Total VMs Possible 33 66 72 73 73 100 100 200
Max VM per Blade (4GB DIMMs) 16 64 24 32 21 16 24 42
Max VM per Chassis (4GB DIMM) 128 256 192 256 147 256 384 336
Max VM per Blade (8GB DIMMs) 32 66 48 64 42 32 48 85
Max VM per Chassis (8GB DIMM) 256 264 384 512 294 512 768 680

More on Cisco UCS, HP Matrix and ITaaS

I just finished reading Project California: a Data Center Virtualization Server – UCS (Unified Computing System) from Cisco. It gave an excellent take on Cisco’s view of how UCS benefits a datacenter. It also explains how new technologies from Intel, QLogic and Emulex all complement the Cisco gear. As a matter of fact, the first four chapters are all about the complementing technologies. Obviously, it is all twisted into a nice package that Cisco offers as their Unified Computing System. Its a great, educational geek book.

The UCS depends on several enabling technologies, like FCoE. FCoE allows you to take your existing Fibre Channel investment and send it down an ethernet channel. A big FAT 10GbE channel. The benefit here is that you can have eight cables feed everything to eight blades and have a nice neat rack. But Scott Lowe points out some limitations on his blog. Right now, it appears that Cisco’s FCoE will terminate at the top of the rack with the Nexus 5000. The book explains how iSCSI is a great alternative and you don’t even need a CNA to make that work, but you need an iSCSI interface on the storage system. So the UCS requires change at some point in the data path.

The HP Matrix is really just the C-Class blade offering coupled with the software to enable management and orchestration, both are important aspect that I believe will assist in making Cloud Computing a reality. The beauty part of the C-Class Blades is that you can keep using Fibre Channel and Ethernet as separate entities, so you don’t really need to make a change in order to use them. The problem is that it doesn’t seem that HP has a mezzanine available to provide FCoE, or some of the virtualization technologies, like SRIOV, VNTag, etc. So, if you want to jump on the FCoE bandwagon or start using some of the neat new networking toys, you will need to wait for a bit.

So, there’s some things about storage, what about networking? Well, the UCS uses what is termed a Fabric Interconnect, which is described as a multiplexer that funnels the sixteen 10GbE ports from the blades down to eight 10GbE uplink ports. I am taking this to be their version of HP’s Virtual Connect, with the added benefit of transferring all of those little Cisco features right up to the Nexus 1000-V dvSwitch. This returns control of the complete network path back to the network admins. This gives the network admins the ability to set up things like policies at the VM level. These settings will follow the VM during VMotion activities, which should allow for a more efficient network.

HP only offers Virtual Connect if you want 10GbE switching within the chassis. Don’t misunderstand me, there is absolutely nothing wrong with Virtual Connect. I have even set them up in (traditionally) Cisco networks. But there are also politics involved when choosing the networking. If HP wants to tout flexibility with interconnects, they may want to make nice with Cisco and come up with a Nexus offering. Or is this a case of Cisco taking their ball and going home to try to force people to buy UCS? I don’t know a lot about Dell Blades, but I don’t see a Cisco 10GbE there either. I used to hear the quip that all of the winders, Linux and Unix boxes are just I/O attached to the Mainframe. Is this a case of the x64 boxes being just I/O attached to the network?

As for ITaaS, both UCS and HP offer some pretty software to allow for management and orchestration. Both have their plusses and minuses (C’mon Cisco… Java? Really?!?) This could be where HP has a big leg up on Cisco. With all of their management software having the same look and feel, on-the-fly dynamic changes can take place with less sdministrator interaction. I’m not so sure CIsco can allow you to provision server, network and storage from the OS to the LUN. Like I said Cloud Computing won’t become a commonplace reality until all of the moving parts can be managed, monitored and provisioned (Orchestration). I’m still not convinced that HP software will allow me to create a RAID/Disk group and provision storage on an EMC box. I’m not so sure that Cisco will play nice in a Brocade fabric and allow for all of the Brocade specific features. And what about someone that chooses to (*GASP*) install an OS directly on the blade? I know that I can provision any hypervisor or winders or Linux on an HP blade. Can Cisco provide an interface to provision an OS directly on the hardware? How about the ability to have VMware running on a blade today, Xen next week and Linux the following week? All without an administrator mounting a CD or interacting with the installer? And how about having that VMware or Xen or Linux OS jump over to a different blade, with or without service interruption, but without manual intervention? That’s ITaaS. That’s Cloud Computing.

DISCLAIMER: I work for a company that is both an HP Partner and a Cisco Partner. These are my opinions, not theirs. Also, I did not pay for the book, but that did not influence this post either.