Yellow Bricks

by Duncan Epping

Storage

vSphere 5.1 All Paths Down (APD) enhancements

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I’ve written about Permanent Device Loss multiple times but another scenario that some of you might have encountered is All Paths Down. All Paths Down already describes the scenario, but an example would be when for whatever reason the network between the host and the array fails. This would be result in an APD condition, meaning that the LUNs are unreachable due to the fact that all paths to the LUN are gone.

Some of you who have been in this scenario probably also have seen hosts being disconnected. In some cases, I’ve seen this happening at one point, a host might even freeze up. This would typically happen when a lot of I/O was sent to the datastore. This is of course something that everyone would want to avoid and hence a new advanced setting has been introduced, a new mechanism to handle APD conditions.

This brand new setting is called Misc.APDHandlingEnable. It can be set to 0 or 1. A value of zero means that ESXi will stick to the “old” method which is to always retry failed I/O’s. A value of 1 enables the new behavior. The behavior will allow ESXi to “fast-fail” I/Os. This will happen after 140 seconds by default. Fast-failing I/Os is what will prevent the host to be disconnected or frozen up.  This is configurable though through Misc.APDTimeout. Note you can set a filter in the Web Client to find the right advanced setting as shown in the screenshot below. Note that the minimum value for Misc.APDTimeout is 20 seconds.

Cormac Hogan has a great article about APD with a lot more technical details, make sure to read it.

VMworld session report: INF-STO2223 – Tech Preview vSphere Integration with Existing Storage

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A couple of weeks ago I posted an article about Virtual Volumes aka vVOLs. This week at VMworld Thomas (Tom) Phelan and Vijay Ramachandran delivered a talk which again addressed this topic but they added Virtual Flash to the mix. The session was “INF-STO2223”.

For those attending Barcelona, sign up for it! It is currently scheduled once on Wednesday at 14:00.

The session started out with a clear disclaimer, this was a technology preview and there is no guarantee whatsoever that this piece of technology will ever be released.

Tom Phelan covered Virtual Flash and Vijay covered Virtual Volumes but as Virtual Volumes was extensively covered in my other blog post I would like to refer back to that blog post for more details on that topic. This blog post will discuss the “Virtual Flash” portion of the presentation, virtual flash or vFlash in short is often also called “SSD caching”.

The whole goal of the Virtual Flash project is to allow vSphere to manage SSD as a cluster resource, just like CPU and memory today. Sounds familiar right for those who read the blog post about vCloud Distributed Storage?! The result of this project should be a framework which allows partners to insert their caching solution and utilize SSD resources more effectively without some of the current limitations.

Virtual Flash may be VM-transparent but also VM-aware. Meaning that it should for instance be possible to allocate resources per virtual machine or virtual disk. Some controls that should be included are reservations, shares and limits. On top of that, it should fully work with  vMotion and integrate with DRS.

Two concepts were explained:

  1. VM transparent caching
  2. VM-aware caching

VM transparent caching uses a hypervisor kernel caching module which sits directly in the virtual disk’s data path. It can be used in two modes, write thru cache (read only) and write back cache (read and write). On top of that it will provide the ability to migrate cache content during a vMotion or discard the cache.

VM-aware caching is a type of caching where the Virtual Flash resource is presented directly to the virtual machine as a device. This allows the virtual machine to control the caching algorithm. The cache will in this case automatically “follow” the virtual machine during migration. It should be pointed out that if the VM is powered off the cache is flushed.

For those managing virtual environments, architecting them or providing health check services… think about the most commonly faced problem, yes that typically is storage performance related. Just imagine for a second having a caching solution at your disposal which could solve most of these problems…. Indeed that would be awesome. Hopefully we will hear more soon!

INF-STO2192 – Tech Preview of VMware Distributed Storage

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I could visit just one session on Tuesday so I decided I would attend a session which is on a topic that I love “Software Defined Storage”, aka vCloud Distributed Storage. This session was hosted by Christos Karamanolis and Kiran Madnani. Christos is one of the lead engineers on the project and Kiran is the product manager, both VMware employees.

Before I lay down what their session was about, note that this was a technology preview. No commitments have been made when or even IF this will ever be released… but as the demo looked so promising I figured it was worth sharing.

[Edit: Cormac Hogan published the demo, worth watching!]

Kiran started out with explaining the journey to Software Defined Storage. Awesome features he mentioned were Storage vMotion, Storage DRS, SIOC, Profile Driven Storage, vSphere Replication and more. Kieran made a statement which I can only agree with….

The world is changing, compute resource keep growing, data keeps on growing!

[Read more…] about INF-STO2192 – Tech Preview of VMware Distributed Storage

Virtualization Changes Everything: Storage Strategies for VMware vSphere & Cloud Computing

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A long long time ago Vaughn Stewart reached out to me and asked me if I wanted to write a foreword for his book. When Vaughn told me the topic I knew this was going to be a hit! For several reasons it took a while for the book to be released but now it finally is available. Vaughn and Michael Slisinger did an excellent job and I would recommend everyone who is interested in storage / virtualization / cloud to pick it up. I love the fact they went the self-publishing route and decided to make it available for $ 19.95 (print) and just $ 9.99 (location dependent pricing, so may vary) for the ebook! I would recommend everyone to pick up the ebook though, GO VIRTUAL!

I want to thank Mike and Vaughn for the opportunity to write the foreword, and congrats on the release… I hope you will sell millions.

Storage is a foundational component in the support of virtualization and cloud computing – and it is dynamically evolving. It is an aspect of the datacenter that is all-too-often overlooked, but without storage, there is no data, and without data, there is no cloud. Virtualization Changes Everything, by Vaughn Stewart and Mike Slisinger, examines the evolutionary influence of host virtualization and cloud computing in breaking storage deployment out of outdated silo models and into a dynamic, flexible hosting environment. Virtualization Changes Everything reviews common goals and challenges associated with providing storage service with cloud computing, and addresses each through the application of advanced storage technologies designed to scale in order to support the ever-expanding storage needs of the future. The examples within the book are pulled from real-world experience, and often involve the integration of multiple innovative technologies. If you are looking for measured guidance on high availability, efficiency, integration and performance for the storage in your cloud, then this book is for you!

 

Introducing SimpliVity, a new storage / compute platform

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Around VMworld many new companies are “born”… well most of them have been around for a while, but fact is that they go public around VMworld. With SimpliVity it is no different. SimpliVity is a new storage company, although “storage” might be understating what they actually do.

I had an intro to SimpliVity last week, and yesterday SimpliVity publicly announced their product the OmniCube. The OmniCube is a 2U unit which combines Compute and Storage resources in a single node combining SATA and SSD drives.

Yes I can hear you thinking aahhhh another Nutanix-alike solution… well not really and I will explain why in the upcoming paragraphs. I guess the biggest difference from a physical perspective is that this is not a multi-node 2U unit like Nutanix is. This is a single node 2U unit, it can hold a max of 768GB of memory but comes with 128GB by default. It holds two 6 core 2.5Ghz intel procs and 2 x 10Gbe and 2 x 1Gbe. From a storage perspective it comes with 4 x 200GB SSD and 8 x 3TB SATA drives. With deduplication and compression, usable capacity is around 20TB. This was calculated using conservative estimates for deduplication (1.5:1) and compression (1.5:1). Depending on the use case this is more than likely a lot higher. Yes the OmniCube is a beast.

But SimpliVity / OmniCube is not about hardware, SimpliVity in my opinion is really about the solution. SimpliVity took a VM centric approach, or should we say VM aware (Not unlike Tintri). All operations / policies are on a per VM basis. So if you want to enable replication, this will be on a per VM basis. Not just replication but they have added a whole bunch of other cool features like:

  • Global management
  • Snapshots
  • Deduplication / Compression (global!)
  • Cloud Integration

The cool thing of course that these features can be combined. Having your snapshots deduplicated will have an impact on the amount of data stored. Only replicating deduplicated and compressed blocks will lower your bandwidth requirements… and that especially comes in handy when you are replicating / storing data in a cloud environment as the dedupe / compression is on a global basis.

Combine all of that with a tight VMware vSphere integration and I believe we have a very interesting solution on our hands. Now I know some of you are skeptical about these new companies popping up, and I can also be skeptical but a quick search on linkedin reveals where these guys are coming from… and with most of their engineers having a strong storage and virtualization background you know they will be on top of their game.

Simplivity has a booth at VMworld, for anyone interested in new compute/storage architectures definitely recommended to stop by, or register for their session:

SPO3287 – Everybody Wants to Rule the World. 5 Steps to Successfully Building and Ruling a Virtual Infrastructure Empire

Cormac also posted a nice article on this topic, make sure to read it!