Yellow Bricks

by Duncan Epping

best practice

VMware HA Deployment Best Practices

· ·

Last week VMware officially released an official paper around Deployment Best Practices for HA. I was one of the authors of the document. Together with several people from the Technical Marketing Team we gathered all best practices that we could find, validated and simplified them to make it rock solid. I think it is a good read. It is short and sweet and I hope you will enjoy it.

Latest Revision:
Dec 9, 2010

Download:
http://www.vmware.com/files/pdf/techpaper/VMW-Server-WP-BestPractices.pdf

Description

This paper describes best practices and guidance for properly deploying VMware HA in VMware vSphere 4.1.  These include discussions on proper network and storage design, and recommendations on settings for host isolation response and admission control.

Storage IO Control Best Practices

· ·

After attending Irfan Ahmad’s session on Storage IO Control at VMworld I had the pleasure to sit down with Irfan and discuss SIOC. Irfan was so kind to review my SIOC articles(1, 2) and we discussed a couple of other things as well. The discussion and the Storage IO Control session contained some real gems and before my brain resets itself I wanted to have these documented.

Storage IO Control Best Practices:

  • Enable Storage IO Control on all datastores
  • Avoid external access for SIOC enabled datastores
    • To avoid any interference SIOC will stop throttling, more info here.
  • When multiple datastores share the same set of spindles ensure all have SIOC enabled with comparable settings and all have sioc enabled.
  • Change latency threshold based on used storage media type:
    • For FC storage the recommended latency threshold is  20 – 30 MS
    • For SAS storage the recommended latency threshold is  20 – 30 MS
    • For SATA storage the recommended latency threshold is 30 – 50 MS
    • For SSD storage the recommended latency threshold is 15 – 20 MS
  • Define a limit per VM for IOPS to avoid a single VM flooding the array
    • For instance limit the amount of IOPS per VM to a 1000

Storage I/O Fairness

· ·

I was preparing a post on Storage I/O Control (SIOC) when I noticed this article by Alex Bakman. Alex managed to capture the essence of SIOC in just two sentences.

Without setting the shares you can simply enable Storage I/O controls on each datastore. This will prevent any one VM from monopolizing the datatore by leveling out all requests for I/O that the datastore receives.

This is exactly the reason why I would recommend anyone who has a large environment, and even more specifically in cloud environments, to enable SIOC. Especially in very large environments where compute, storage and network resources are designed to accommodate the highest common factor it is important to ensure that all entities can claim their fair share of resource and in this case SIOC will do just that.

Now the question is how does this actually work? I already wrote a short article on it a while back but I guess it can’t hurt to reiterate thing and to expand a bit.

First a bunch of facts I wanted to make sure were documented:

  • SIOC is disabled by default
  • SIOC needs to be enabled on a per Datastore level
  • SIOC only engages when a specific level of latency has been reached
  • SIOC has a default latency threshold of 30MS
  • SIOC uses an average latency across hosts
  • SIOC uses disk shares to assign I/O queue slots
  • SIOC does not use vCenter, except for enabling the feature

When SIOC is enabled disk shares are used to give each VM its fair share of resources in times of contention. Contention in this case is measured in latency. As stated above when latency is equal or higher than 30MS, and the statistics around this are computed every 4 seconds, the “datastore-wide disk scheduler” will determine which action to take to reduce the overall / average latency and increase fairness. I guess the best way to explain what happens is by using an example.

As stated earlier, I want to keep this post fairly simple and I am using the example of an environment where every VM will have the same amount of shared. I have also limited the amount of VMs and hosts in the diagrams. Those of you who attended VMworld session TA8233 (Ajay and Chethan) will recognize these diagrams, I recreated and slightly modified them.

The first diagram shows three virtual machines. VM001 and VM002 are hosted on ESX01 and VM003 is hosted on ESX02. Each VM has disk shares set to a value of 1000. As Storage I/O Control is disabled there is no mechanism to regulate the I/O on a datastore level. As shown in the bottom by the Storage Array Queue in this case VM003 ends up getting more resources than VM001 and VM002 while all of them from a shares perspective were entitled to the exact same amount of resources. Please note that both Device Queue Depth’s are 32, which is the key to Storage I/O Control but I will explain that after the next diagram.

As stated without SIOC there is nothing that regulates the I/O on a datastore level. The next diagram shows the same scenario but with SIOC enabled.

After SIOC has been enabled it will start monitoring the datastore. If the specified latency threshold has been reached (Default: Average I/O Latency of 30MS) for the datastore SIOC will be triggered to take action and to resolve this possible imbalance. SIOC will then limit the amount of I/Os a host can issue. It does this by throttling the host device queue which is shown in the diagram and labeled as “Device Queue Depth”. As can be seen the queue depth of ESX02 is decreased to 16. Note that SIOC will not go below a device queue depth of 4.

Before it will limit the host it will of course need to know what to limit it to. The “datastore-wide disk scheduler” will sum up the disk shares for each of the VMDKs. In the case of ESX01 that is 2000 and in the case of ESX02 it is 1000. Next the  “datastore-wide disk scheduler” will calculate the I/O slot entitlement based on the the host level shares and it will throttle the queue. Now I can hear you think what about the VM will it be throttled at all? Well the VM is controlled by the Host Local Scheduler (also sometimes referred to as SFQ), and resources on a per VM level will be divided by the the Host Local Scheduler based on the VM level shares.

I guess to conclude all there is left to say is: Enable SIOC and benefit from its fairness mechanism…. You can’t afford a single VM flooding your array. SIOC is the foundation of your (virtual) storage architecture, use it!

ref:
PARDA whitepaper
storage i/o control whitepaper
vmworld storage drs session
vmworld storage i/o control session

Re: VMware vSphere 4 default installation settings (gabesvirtualworld)

· ·

In response to Gabes article on default installation settings there are some things I personally almost always do different and I wanted to point them out. Consider them my recommendations / best practices and not necessary VMware’s. I’ve added two (*) and have a different opinion on some of Gabe’s best practices (-)

COS Memory:

  • Although COS memory is “dynamic” I still always increase it to the full 800. The overhead of this in most of the servers(usually always 48GB+) is tiny. (-)

Host Configuration:

  • Hostnames in lowercase characters; to avoid any HA issues. (*)
  • I never change the name of the Service console portgroup, people are used to this name changing it leads to confusion in most cases and it is a critical part of your host. (-)
  • Avoid using agents within the Service Console. (*)

vSwitch settings:

  • Mac address changes: Reject (-)
    A best practice recommended by VMware PSO to ensure that when someone changes a MAC within the OS all inbound packets are dropped.
  • Forged Transmit: Reject (-)
    Setting Forged Transmits to reject ensures that the originator of the packet is validated. Any outbound frame with a MAC address that is different from the one currently set on the adapter will be dropped. Again a best practice recommended by VMware PSO.

Single Initiator Zoning, recommended or not?

· ·

A question we receive a lot is what kind of zoning should be implemented for our storage solution? The answer is usually really short and simple: at least single initiator zoning.

Single initiator zoning is something we have always recommend in the field (VMware PSO Consultants/Architects) and something that is clearly mentioned in our documentation… at least that’s what I thought.

On page 31 of the SAN Design and Deploy guide we clearly state the following:

When a SAN is configured using zoning, the devices outside a zone are not visible to the devices inside the zone. When there is one HBA or initiator to a single storage processor port or target zone, it is commonly referred to as single zone. This type of single zoning protects devices within a zone from fabric notifications, such as Registered State Change Notification (RSCN) changes from other zones. In addition, SAN traffic within each zone is isolated from the other zones. Thus, using single zone is a common industry practice.

That’s crystal clear isn’t it? Unfortunately there’s another document floating around which is called “Fibre Channel SAN Configuration Guide” and this document states the following on page 36:

  • ESX Server hosts that use shared storage for virtual machine failover or load balancing must be in one zone.
  • If you have a very large deployment, you might need to create separate zones for different areas of functionality. For example, you can separate accounting from human resources.

So which one is correct and which one isn’t? I don’t want any confusion around this. The first document, the SAN Design and Deploy guide is correct. VMware recommends single initiator zoning. Of course if you want to do “single initiator / single target” that would even be better, but single initiator is the bare minimum. Now let’s hope the VMware Tech Writers can get that document fixed…