Skip to main content

When marketing and technical information meet: Hyper-V


While reading an article about Hyper-V per-VM CPU settings, I saw this in the FAQ:


[BEGIN QUOTE]

Why do you use percentage for the limit and reserve – and not MHz / GHz?

Many people find it easier to think in MHz / GHz rather than percentage of a physical computer. They also argue that using a percentage means that as you move a virtual machine from computer to computer you may get different amounts of resource depending on the underlying capability.

This is something that has been discussed extensively on the Hyper-V team, and while I do believe there is some merit in this approach, there are a number of reasons why we chose to use a percentage instead. Two key ones are:

  1. Predictable mobility

    If all your virtual machines have a reserve of 10% – you know that you can run 10 of them on any of your servers. The same would not be true if they all had a reserve of 250Mhz. Given how important virtual machine mobility is to our users – we believe that this is something that needs to be easy to manage.
  2. Not all MHz are the same

    1GHz on a Pentium IV is much slower than 1GHz on a Core i7. Furthermore – newer processors tend to be more efficient at virtualization than older processors, so the difference between the “bang for buck” that you get out of each MHz varies greatly between processor types. This means that in reality – defining a reserve or limit in MHz / GHz does not really give you a great performance guarantee anyway.

[END QUOTE]
Even though this seems to be a list of technical arguments, the claims made are non-sensical:
  1. "we use a relative percentage instead of a fixed unit because we want you to be sure you can run a certain number of guests on any CPU." What ?? Who says that my VMs will actually still run when they suddenly get only half of the power they needed, because they were moved to a CPU with half the horsepower ? A reserve is supposed to be a guarantee, a limit is supposed to be just that: a limit. Even the examples they give for using a reserve or a limit would fail. A misbehaving app that sucks CPU, will suddenly be allowed to use even more, just because it's now running on a faster CPU.
  2. "Not all MHz are the same." That's not a very good reason to use percentages instead, is it. Are they claiming that every % _is_ the same ?
Dear Microsoft (and any other company reading this), please make your technical information technical, and correct. Do whatever you want with your marketing docs, but don't let the marketing seep into the technical documentation.

Comments

Popular posts from this blog

How to solve "user locked out due to failed logins" in vSphere vMA

In vSphere 6, if the vi-admin account get locked because of too many failed logins, and you don't have the root password of the appliance, you can reset the account(s) using these steps:

reboot the vMAfrom GRUB, "e"dit the entry"a"ppend init=/bin/bash"b"oot# pam_tally2 --user=vi-admin --reset# passwd vi-admin # Optional. Only if you want to change the password for vi-admin.# exitreset the vMAlog in with vi-admin These steps can be repeated for root or any other account that gets locked out.

If you do have root or vi-admin access, "sudo pam_tally2 --user=mylockeduser --reset" would do it, no reboot required.

Volkswagen UHV bluetooth touch adapter & its problems

My Volkswagen car has the "universal cellphone preparation" UHV built-in. This is the main part of a car kit, but requires an additional adapter for connecting to a cellphone. At first, I was using an adapter for my good old Nokia 6310, even after I changed to the Nokia E71. Connecting was easy: pair the phone with the "VW UHV" bluetooth entity, and done. This has the phone connected to the car kit at all times, so even non-call-related functions use the car audio system (e.g. voice recognition).
But progress will have its way, no matter what happens. So in comes the "bluetooth touch adapter". Instead of a phone-specific adapter, this is a small touchscreen device that slots into the UHV dashboard mount. Connecting a phone is very different now:
the Bluetooth Touch Adapter connects to the "VW UHV" device via bluetooth
the phone connects to "Touch Adapter" device, also via bluetoothThe device doesn't allow step 2 if step 1 didn't s…

Multiple VLANs on a Synology NAS

Synology, like other SOHO/SMB NAS vendors, touts VLAN functionality with their current DSM 4.1 software. However, the web interface just lets you specify one VLAN tag to use over each eth interface (or bond interface).
Manual approachIn the busybox environment that you can ssh into as root (after enabling ssh through the webinterface), there's all the tools you need to use multiple VLANs over one link (eth or bond), however:
First you insert the 802.1q module into the Linux kernel:
 /sbin/lsmod | /bin/grep -q 8021q || /sbin/insmod /lib/modules/8021q.koThen you add each VLAN you need to every interface (bond0 in this example)
 /sbin/vconfig add bond0 4And finally you can configure IP addresses on every interface.vlan combination (bond0.4 in this example)
 /sbin/ifconfig bond0.4 192.168.4.1 broadcast 192.168.4.255 netmask 255.255.255.0The same type of script would work on a QNAP NAS too, by the way. They offer 8021q.ko and vconfig in their commandline environment as well.
Packets from…