One of the software-defined technologies that have gained tremendous momentum in the past couple of years is software-defined storage. Most hardware and software companies are jumping on the bandwagon to offer software-defined storage solutions. Software-defined storage offers great benefits for housing your production virtualized workloads.
The dominant leader in the enterprise data center when it comes to software-defined storage is VMware vSAN. VMware vSAN is continuing to pick up many new customers with each new release.
The features and functionality with each new release of vSAN continue to raise the bar for competitors to the product.
VMware was a pioneer of the Software-Defined Data Center SDDC concept which it coined back in to virtualize all aspects of the data center including compute, network, and storage. The software-defined data center is the new mindset moving forward that allows your business to be as agile, automated, and abstracted from underlying hardware infrastructure as possible.
As one of the foundational pillars of your SDDC, software-defined storage is at the heart of your data. By using automation and storage pooling, this allows abstracting the hardware from the storage solution and easily pooling resources between servers.vSAN 7 Technical Overview
This allows your environment to gain many benefits using VMware vSAN, including easily scaling up and scaling out as a mechanism that is built right into the vSAN solution and in essence, is now built into the vSphere solution in general as part of the hypervisor itself and vCenter Server.
VMware vSAN allows you to move beyond the traditional concept of storage LUNs that were extremely labor-intensive to change, grow, or reconfigure. In times past, this generally meant destroying the original LUN and reprovisioning a new LUN with new characteristics. When a virtual machine is provisioned you can choose a VM storage policy to support the application that is running on a particular virtual machine.
With the appropriate storage policy selected, SPBM makes sure the virtual machine is allocated the resources needed and is provisioned on the correct tier of storage configured based on the performance and other characteristics. VMware vSAN is an object-based storage solution. Each component of the virtual machine is created as an underlying virtual machine object.
Each object is an individual block storage device. Components are pieces of the VM objects that are stored on a particular cache or capacity device. The maximum number of components per host limit is How are the objects and components laid out physically across the vSAN environment?
VMware vSAN takes care of the layout of vSAN objects automatically and bases the placement decisions based on a number of factors including:.
This provides many tremendous benefits when thinking about configuring and provisioning the vSAN solution. It is a native part of VMware vSphere. As mentioned previously, vSAN is integrated into the hypervisor as a kernel-based solution.
This means there are no additional installations that are required or needed. It is part of vSphere. How does VMware vSAN provide the availability and performance of the software-defined storage solution in a vSphere environment?
VMware VSAN – 3-nodes mode
This allows VMware vSAN to withstand failures of the underlying infrastructure and still maintain the resiliency of your data. This could be anything from a failed disk drive cache or capacity or a failure in the network network card, etc.VSAN is pretty new to me.
I was trying to understand the space requirements for RAID-1 shown in the table given in the white paper page 7. The total capacity in the above table means the total required space capacity in all the disks for storing all of the exact copies here exact means the copy should be as the same size as the original object.
However, the number of minimum hosts should be 2 the same as the minimum number for RAID-1instead of 3 in the table. Host1 and host2 stores the full copies of the VM, and host3 witness for quorum stores pure metadata. Each disk has a vote to vote for the disk which can take over the service. If host1 is down, one full copy is on host2 and two votes are from host2 and host3.
If host2 is down, one full copy is on host1 and two votes are from host1 and host3. If host3 is down, two full copies are on host1 and host2. Two votes are from host1 and host2. We assume one disk component in the example for understanding easily. With this change, witness could be eliminated since one component can have more than 1 vote.
You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account.
You are commenting using your Facebook account. Notify me of new comments via email. Notify me of new posts via email. So If host1 is down, one full copy is on host2 and two votes are from host2 and host3. Share this: Twitter Facebook. Like this: Like LoadingThis question was asked on the VMTN community forum and it is a very valid question.
Our documentation explains this scenario, but only to a certain level and it seems to be causing some confusion as we speak. To be honest, it is fairly complex to understand. Internally we had a discussion with engineering about it and it took us a while to grasp it. As the documentation explains, the failure scenarios are all about maintaining quorum.
If quorum is lost, the data will become inaccessible. This makes perfect sense, as vSAN will always aim to protect the consistency and reliability of data first. SFTT can be seen as host failures, and you can define this between 0 and 3. Now, if you have 1 full site failure, then on top of that you can tolerate SFTT host failures. Where this gets tricky is when the Witness fails, why?
Well because the witness is seen as a site failure. I hope that makes sense? The total vote count is 9.
Which means that the object will be accessible as long as the remaining vote count is 5 or higher. Now that the witness has failed, as shown in the next diagram, we lose 3 votes of the total 9 votes, no problem as we need 5 to remain access to the data. In the next diagram another host has failed in the environment, we now lost 4 votes out of the 9. Which means we still have 5 out of 9 and as such remain access.
And there we go, in the next diagram we just lost another one host, in this case it is the same location as the first host, but this could also be a host in the secondary site. Either way, this means we only have 4 votes left out of the 9. We needed 5 at a minimum, which means we now lose access to the data for those objects impacted. The same applies to RAID-6 of course. With RAID-6 as stated you can tolerate 1 full site failure and 2 host failures on top of that, but if the witness fails this means you can only lose 1 host in each of the sites before data may become inaccessible.
I hope this helps those people running through failure scenarios. Each site will have an equal number of votes and there will be an even distribution of votes within a site.
Duncan, why is Vsan Essentials 2d edition no longer available on Safari? Where can I buy a hard copy? How is the replicated encrypted data ,decrypted on the Second Vcenter? Thank you so much for the reply Ducan, real life saver!
4 Node VSAN Cluster: RAID-1 vs RAID-5
Thanks for the book linkit was ,and is a great resource for my VSAN implementation. So, prefered site will have 5 votes, secondary 4 votes.Had a question recently around the failure scenarios in vSAN.
Should FTT tolerance increase accordingly? Let's have a look a little closer as to how this works. The discussion today is mainly on data placement, not compute. It is assumed that with compute, if the failure happens on the node where there is compute, it is a given that the VM is rebooted on another host except of course it is in FT mode.
4 Node VSAN Cluster: RAID-1 vs RAID-5
Assuming we have a typical 3-node setup with each node having 2 capacity disks. As you can see, there will be 2 set's of mirrored data and a witness component. Witness component is used to prevent a split-brain scenario. When a failure happens to a node completely, it will look something like the diagram above. Given that we have still a good copy of data available, there will not be any impact to production IO's.
However, having said that, vSAN will not necessarily have resources to repair and rebuild the replacement copy. This is because, we will need a minimum of 3 different nodes to place the data. Node failures are rare, so lets look at a more common scenario where a drive with the data fails. The diagram below shows how data is recreated on the other surviving drive on the same node. Now, lets look at a 4-node setup. The following diagram shows a a single node failure in a 4-node cluster.
It looks fairly similar to a 3-node setup with the exception that with a 4-node cluster, data can be rebuilt immediately on the remaining node. Lets change it up slightly. So as you can imagine, in a large cluster where VM's and data is spread out fairly evenly, if a failure exceeds the defined FTT policy, there is a possibility that some VM's may be affected, and some will continue as usual.
The screenshot below shows a 4-node cluster with 2 node failures. Dummy1 VM is still in "Reduced availability with no rebuild" because it has at least 2 of 3 surviving components. Dummy2 VM on the other hand, have failed 2 of 3, hence its showing "Inaccessible".
So back to the first question, as the cluster grows, is it wise to extend the FTT policy?Can you give us some detail on calculating Disk Yield? If I have 3 modes with 1tb, will I see 3 tb storage? There should be a sizing guide going live shortly, but all magnetic disks across all the hosts will contribute to the size of the VSAN datastore.
The SSDs or flash devices do not contribute to capacity. Hope that makes sense. Lots of documentation coming around this. Are you saying that it will consume an additional GB of space due to the 2 replicas created? Yep — you got it. This file was introduced in 5. Does this file belong in the swap object?
Is there a second swap object for it? Or does it simply belong to the VM namespace object? Yes — this is what we are referring to. This is now instantiated as its own object on the VSAN datastore, and does not consumes space in the VM namespace object. It is specified as a percentage of the logical size of the virtual machine disk object.
So a percentage of the logical size used storage. The example on page 47 takes the flash read cache reservation as a percentage of the physical space allocated storage. What is the truth? These statements are meant to reflect the same thing Stevin. However, whether you use that or not, you request a VMDK size during provisioning, e. Now you may only use a portion of this, e. Hopefully that makes sense.
The book states: In the initial version of VSAN, there is no proportional share mechanism for this resource when multiple VMs are consuming read cache, so every VM consuming read cache will share it equally.
Every write has to go through the write cache i presume? How is write cache shared between VMs? If I copy a large file from :C to D: drive in my windows VM, I see very poor transfer rates by comparison to the same copy on a PC less than half the speed. The transfer rate drops to zero for up to 7 seconds for periods during the transfer.
Its almost like its cache allocation has filled up and its waiting for destage to complete. I would recommend opening a call with support. Are you running this? It is completely dependent on the VMs that you deploy.
Appreciate Cormac, understand the ratio will determine the performance. And user configure it with their application case. The ratio here I mentioned is physical device number not capacity number. If all of your writes are hitting the cache layer, and all of your reads are also satisfied by the cache layer, and destaging from flash to disk is working well, then ratio will work just fine.
If however you have read cache misses that need to be serviced from HDD, or there is a large amount of writes in flash that need to be regularly destaged from flash to HDD, then you will find that a larger ratio, and the use of striping across multiple HDDs for your virtual machine objects can give better performance.
Yes, Cormac.Here is a brief statement summarizing my opinion on the topic.
You should reexamine the requirements and decisions that were made during the design of the cluster. The decision to configure a 4 node cluster with a specific set of cache drives and capacity drives are typically based on requirements to deliver to a specific amount of usable storage with a specific level of availability. In other words, whenever a host is offline for a significant amount of time, you can rebuild data and be protected in case of the failure of another host.
Its required minimum number of nodes is 4, which your cluster has. In other words, whenever a host is offline for a significant amount of time, you will not be able to rebuild data and you are not fully protected in event of the failure of another host.
If you want the benefit of reduced storage consumption but want to maintain the current level of availability, consider adding a 5th node to the cluster prior to implementing VSAN RAID In this case, is it possible another ESXi fail in the cluster?
In your scenario, after the rebuild, assuming you now have 9 surviving hosts and plenty of space, your VMs should be fully protected again and ready to survive another single host failure.
Thanks johnnyadavis. So, how many failure hosts could support the cluster? Are there any way to do this calculate? The number of supported hosts failures is a per-VM consideration. You can use the vSphere Client to check compliance and make use of associated alarms that are triggered when an object is not in compliance. If you build a cluster that meets or exceeds the vSAN recommendations, the you should expect each VM that is compliant with its storage policy to be protected against host failures per its FTT setting.
When you attempt to place a host into maintenance mode, the wizard will prompt you concerning evacuating data. If you successfully, fully evacuate, then all your VMs should still be fully protected at their FTT level, but the operation could take a long time. If you choose not to fully evacuate, the wizard warns you concerning the number of VMs that will become inaccessible and the number of VMs that will become non-compliant. You are commenting using your WordPress.
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Email required Address never made public. Name required. Examining Health of a vRA 7.This policy plays an important role when planning and sizing storage capacity for Virtual SAN. The default FTT is equal to onewhich means that the system can tolerate a single failure within a cluster.
It can be a disk drive, host failure, or processor etc. With a single failure, two copies of the data are needed. Now, how about looking at a four-node cluster in which the fourth host is there in case we have unpredicted hardware problems? The recommended number of hosts for VSAN cluster is four. In case there is a single host failure, the system recreates the object from the failed host, putting it on the remaining host within the cluster—the fourth one.
Thus, the recommended number of hosts to have is four. You have a failure on another host within your cluster; however, it is fine because you still have two remaining hosts assuring the balance, but no components can be recreated on another host there are no more hosts available.
We can see a failed host below. After the resynchronization, the cluster can protect workloads against single failures again. I assume you have a vCenter server installed and running. I also assume that you have already created a datacenter object and a cluster object within the UI. The walkthrough will show the configuration using vSS. Then, choose the first radio buttonVMkernel Network Adapter. Next, we can use the existing standard switch. Choose the New standard switch radio button. VSAN network configuration wizard - New standard switch.
We can now add a physical adapter to be used for VSAN traffic. Click OK to validate. VSAN network configuration wizard - Ready to complete. Next, we can see the new VMkernel adapter we have just created. If the requirements discussed earlier at least one SSD and at least one HDD in a disk group were fulfilled, the easiest part comes now.