8.0

Doing network/ISL maintenance in a vSAN stretched cluster configuration!

Duncan Epping · Nov 21, 2023 · 3 Comments

I got a question earlier about the maintenance of an ISL in a vSAN Stretched Cluster configuration which had me thinking for a while. The question was what would you do with your workload during maintenance. I guess the easiest of course is to power off all VMs and simply shutdown the cluster, for which vSAN has a UI option, and there’s a KB you can follow. Now, of course, there could also be a situation where the VMs need to remain running. But how does this work when you end up losing the connection between all three locations? Normally this would lead to a situation where all VMs will become “inaccessible” as you will end up losing quorum.

As said, this had me thinking, you could take advantage of the “vSAN Witness Resiliency” mechanism which was introduced in vSAN 7.0 U3. How would this work?

Well, it is actually pretty straight forward, if all hosts of 1 site are in maintenance mode, failed, or powered off, the votes of the witness object for each VM/Object will be recalculated within 3 minutes. When this recalculation has completed the witness can go down without having any impact on the VM. We introduced this capability to increase resiliency in a double-failure scenario, but we can (ab)use this functionality also during maintenance. Of course I had to test this, so the first step I took was placing all hosts in 1 location into maintenance mode (no data evac). This resulted in all my VMs being vMotioned to the other site.

Now next I checked with RVC if my votes were recalculated or not. As stated, depending on the number of VMs this can take around 3 minutes in total, but usually will probably be quicker. After the recalculation had been completed I powered off the Witness, and this was the result as shown below, all VMs were still running.

Of course, I had to double check on the commandline using RVC (you can use the command “vsan.vm_object_info” to check a particular object for instance) to ensure that indeed the components of those VMs were still “ACTIVE” instead of “ABSENT”, and there you go!

Now when maintenance has been completed, you simply do the reverse, you power on the witness, and then you power on the hosts in the other location. After the “resync” has been completed the VMs will be rebalanced again by DRS. Note, DRS rebalancing (or should rules being applied) will only happen when the resync of the VM has been completed.

vSphere 8.0 U2 and vSAN 8.0 U2 just shipped, learn all about it here!

Duncan Epping · Sep 22, 2023 · 2 Comments

vSphere 8.0 U2 and vSAN 8.0 U2 just shipped, and of course the Unexplored Territory Podcast has already covered this. If you want to learn all about it make sure to listen to the episode below. Or of course read the release notes (vCenter, ESXi, vSAN).

You can find the vSAN 8.0 U2 episode on Spotify (https://bit.ly/3QNjpFk), and Apple (https://bit.ly/3QPt7XL), as well as any other podcast app, or simply listed via the embedded player below!

You can find the vSphere 8.0 U2 episode on Spotify (https://bit.ly/3snOh5l), Apple (https://bit.ly/45lRK2Q), as well as any other podcast app, or simply listed via the embedded player below!

Deleting the vCLS VMs using Retreat Mode starting with vSphere 8.0 U2

Duncan Epping · Sep 22, 2023 · 2 Comments

I posted about “retreat mode” and how to delete the vCLS VMs when needed a while back, including a quick demo. Back then you needed to configure an advanced setting for a cluster if you wanted to delete the VMs for whatever reason. (Usually for troubleshooting purposes people would do a delete/recreate.) Starting with vSphere 8.0 U2 you can now use the UI to enable retreat mode on a per cluster level. How do you do this? well fairly straight forward:

Click on the cluster you would want to delete the VMs for
Click on Configure
Click on “General” under “vSphere Cluster Services”
Click on “EDIT VCLS MODE”
Click on “Retreat Mode” and click “OK”

Now the VMs will be deleted, if you want to recreate the VMs, follow the same procedure, but change “Retreat Mode” to “System Managed”. I tested the process yesterday and created a quick demo for you:

Scalable Snapshots demo with the vSAN 8.0 Express Storage Architecture

Duncan Epping · Sep 5, 2023 · 1 Comment

Starting with vSAN 8 a brand new architecture was introduced called “Express Storage Architecture”. Over the last year or so a lot of information has been shared about ESA and the benefits of ESA. One of the things which ESA introduces is much-improved snapshot scalability.

With vSAN OSA, and with VMFS, when you create a snapshot you typically immediately see a performance degradation. This is because both VMFS and vSAN OSA still operate using the redo-log based snapshot mechanism. This means that with vSAN OSA when you create a snapshot a new object is created and writes are re-directed. It also means that reads will be coming from various files, if you have one or more snapshots. This mechanism is, unfortunately, not very effective. Let me borrow a diagram that is part of a post John Nicholson wrote to demonstrate that old logic.

With vSAN 8 ESA the mechanism has changed and no longer does vSAN, or vSphere for that matter, create an additional object. vSAN ESA handles this on a meta-data level. In other words, instead of redirecting writes and traversing files for reads, vSAN now leverages a highly efficient B-Tree structure and pointers to keep track of which block is associated with which snapshot.

Not only is this more efficient from a capacity perspective, but more importantly it is very efficient from a performance standpoint. I ran half a dozen tests in my lab, and what I saw was a below 2% performance impact between a VM without a snapshot and a VM with one or multiple snapshots. I could NOT see a significant difference between the first or the fifth snapshot. I do want to point out that my lab is not officially certified to run vSAN ESA, nevertheless, I was very impressed with the results.

During the last run, I actually recorded the whole exercise. In this demo, I show the creation of one snapshot, while the VM is running a benchmark (HCIBench). Now, during the testing, I created not one but various snapshots and of course, I deleted all of them as well. You have all probably experienced extensive stun times during the deletion of a snapshot at times, and this is where vSAN ESA shines. The stun times have been reduced by 100 times, and that is something I am sure each of you will appreciate. Why have they been reduced drastically? Well, simply because we no longer have to copy data from one vSAN object to another. This makes a huge difference, not just for stun times, but also for performance in general (latency, IOPS, throughput). If you are interested, have a look at the demo!

MAXimizing vSAN’s potential with the Express Storage Architecture (vSAN Max)

Duncan Epping · Aug 31, 2023 · 4 Comments

Last week at VMware Explore a few vSAN features and offerings were announced, one of them being vSAN Max! All week I have been having conversations with customers who were highly excited about the new solution. For those who did not read the announcements, or listened to the Unexplored Territory Podcast episode on the topic, let me go over what was announced and what vSAN Max is.

As most of you know, vSAN is a hyperconverged storage platform delivered via VMware’s flagship product vSphere. This means that if you have vSphere running, vSAN is literally two clicks away from being enabled. You will need local storage devices, and those local devices then will be formed into a shared datastore on top of which you can run your VMs. Although HCI solutions work for most customers, at certain levels of scale it may be preferred to have a disaggregated solution and share a dedicated storage platform with one or multiple vSphere clusters. This is what vSAN Max brings to the table.

Looking at the above diagram a few things stand out when it comes to vSAN Max. First of all, it says “Storage Only” and secondly it mentions “Supports high-density ESA ReadyNodes”. There are a few things to unwrap here. Firstly, vSAN Max is based on vSAN Express Storage Architecture, aka vSAN ESA. This means that it is a single tier of storage, based on NVMe flash devices. On top of that, it also means that all available data services will also be available on vSAN Max: Fault Domains, Stretched Clustering, vSAN File Services, iSCSI, Compression, Encryption etc. All of these are also included by default in the license by the way, it is just a single edition from a licensing point of view and it will include vSphere. In other words, vSphere + vSAN Enterprise by default, and licensed on capacity instead of CPU/Cores.

Secondly, it mentions “high-density”, vSAN Max starts at 200TB per host, and has a minimum of 6 hosts per cluster. This means that the starting capacity is 1.2 Petabytes for a vSAN Max cluster. The maximum number of hosts within a cluster is 32 at the time of writing (but 24 hosts being the recommended maximum), and it will support up to 8.6 Petabytes and around 3.4 million IOPS.

It also mentions ReadyNodes, and let me stress this, ReadyNodes! We still see a lot of customers picking random components for their vSAN cluster and then being surprised that Skyline Health reports the cluster is not supported. For vSAN Max there will be a separate set of vSAN ReadyNode configurations. These configurations will have for instance 100Gbps network cards, and as mentioned a minimum of 200TB per host.

Now, this doesn’t mean that the connecting clusters need to be running 100GbE, they can be even 1Gbps connected, that’s up to you and the requirements you have from a performance perspective. The 100GbE connections will be used for intra-cluster communications, so the switching architecture also needs to cater to this.

Knowing all of this, you may wonder what the use cases are for vSAN Max. As Pete Koehler mentioned, it can be used for anything, but is primarily targeted at those with high capacity requirements and who prefer a centralized model, but still want to manage their storage platform through vCenter Server and use all the bells and whistles that come with it (and with VROps for instance).

Hopefully, that provides some insights in terms of what to expect when vSAN Max goes “general availability” I will follow up with some short demos showing what it will look like, although that will probably be relatively boring as it will look very similar to vSAN ESA. In the meanwhile, there’s a bunch of material on the VMware website that you can check out.