VSAN VDI Benchmarking and Beta refresh!

26 November, 2013 by 3 Comments

I was reading this blog post on VSAN VDI Benchmarking today on Vroom, the VMware Performance blog. You see a lot of people doing synthetic tests (max iops with sequential reads) on all sorts of storage devices, but lately more and more vendors are doing these more “real world performance tests”. While reading this article about VDI benchmarking, and I suggest you check out all parts (part 1, part 2, part 3), there was one thing that stood out to me and that was the comparison between VSAN and an All Flash Array.

The following quotes show the strength of VSAN if you ask me:

we see that VSAN can consolidate 677 heavy users (VDImark) for 7-node and 767 heavy users for 8-node cluster. When compared to the all flash array, we don’t see more than 5% difference in the user consolidation.

Believe me when I say that 5% is not a lot. If you are actively looking at various solutions, I would highly recommend to include the “overhead costs” to your criteria list as depending on the solution chosen this could make a substantial difference. I have seen other solutions requiring a lot more resources. But what about response time, cause that is where the typical All Flash Array shines… ultra low latency, how about VSAN?

Similar to the user consolidation, the response time of Group-A operations in VSAN is similar to what we saw with the all flash array.

Both very interesting results if you ask me. Especially the < 5% in user consolidation is what stood out to me the most! Once again, for more details on these tests read the VDI Benchmarking blog part 1, part 2, part 3!

Beta Refresh

For those who are testing VSAN, there is a BETA refresh available as of today. This release has a fix for the AHCI driver issue… and it increases the disk group limit from 6 to 7. From a disk group perspective this will  come in handy as many servers have 8, 16 or 24 disk slots allowing you to do 7HHDs + 1 SSD per group. Also some additional RVC commands have been added in the storage policy space, I am sure they will come in handy!

Nice side affect of the number of HDDs going up is increase in max capacity:

(8 hosts * (5 diskgroups * 7 HDDs)) * Size of HDD = Total capacity

With 2 TB disks this would result in:

(8 * (5 * 7)) * 2TB = 560TB

Now keep on testing with VSAN and don't forget to report feedback through the community forums or your VMware rep.

Filed Under: Software Defined, Storage, Virtual SAN Tagged With: , , , , , ,

Startup intro: Coho Data

15 October, 2013 by 1 Comment

Today a new startup is revealed named Coho Data, formerly known as Convergent.io. Coho Data was founded by Andrew Warfield, Keir Fraser and Ramana Jonnala. For those who care, they are backed by Andreessen Horowitz. Probably most known for the work they did at Citrix on Xenserver. What is it they introduced / revealed this week?

Coho Data introduces a new scale-out hybrid storage solution (NFS for VM workloads). With hybrid meaning a mix of SATA and SSD. This for obvious reasons, SATA bringing you capacity and flash providing you raw performance. Let me point out that Coho is not a hyperconverged solution, it is a full storage system.

What does it look like? It is a 2U box which holds 2 “MicroArrays” which each MicroArray having 2 processors, 2 x 10GbE NIC port and 2 PCIe INTEL 910 cards. Each 2u block provides you 39TB of capacity and ~180K IOPS (Random 80/20 read/write, 4K block size). Starting at $2.50 per GB, pre-dedupe & compression (which they of course offer). Couple of things I liked looking at their architecture, first and probably foremost the “scale-out” architecture, scale to infinity is what they say in a linear fashion. On top of that, it comes with an OpenFlow-enabled 10GbE switch to allow for ease of management and again scalability.

If you look closely at how they architected their hardware, they created these highspeed IO lanes: 10GbE NIC <–> CPU <–> PCIe Flash Unit. Each highway has its dedicated CPU, NIC Port, ad on top of that they PCIe Flash, allowing for optimal performance, efficiency and fine grained control. Nice touch if you ask me.

Another thing I really liked was their UI. You can really see they put a lot of thought in the user experience aspect by keeping things simple and presenting data in an easy understandable way. I wish every vendor did that. I mean, if you look at the screenshot below how simple does that look? Dead simple right!? I’ve seen some of the other screens, like for instance for creating a snapshot schedule… again same simplicity. Apparently, and I have not tested this but I will believe them on their word, they brought that simplicity all the way down to the “install / configure” part of things. Getting Coho Data up and running literally only takes 15 minutes.

What I also liked very much about the Coho Data solution is that Software-defined Networking (SDN) and Software-defined Storage (SDS) are tightly coupled. In other words, Soho configures the network for you… As just said, it takes 15 minutes to setup. Try creating the zoning / masking scheme for a storage system and a set of LUNs these days, even that takes more time then 15 – 20 minutes. There aren’t too many vendors combining SDN and SDS in a smart fashion today.

When they briefed me they gave me a short demo and Andy explained the scale-out architecture, during the demo it happened various times that I could draw a parallel between the VMware virtualization platform and their solution which made is easy for me to understand and relate to their solution. For instance, Soho Data offers what I would call DRS for Software-Defined Storage. If for whatever reasons defined policies are violated then Coho Data will balance the workload appropriately across the cluster. Just like DRS (and Storage DRS) does, Coho Data will do a risk/benefit analysis before initiating the move. I guess the logical question would be, well why would I want Coho to do this when VMware can also do this with Storage DRS? Well keep in mind that Storage DRS works “across datastores”, but as Coho presents a single datastore you need something that allows you to balance within.

I guess the question then remains what do they lack today? Well today as a 1.0 platform Coho doesn’t offer replication to outside of their own cluster. But considering they have snapshotting in place I suspect their architecture already caters for it, and it something they should be able to release fairly quickly. Another thing which is lacking today is a vSphere Web Client plugin, but then again if you look at their current UI and the simplicity of it I do wonder if there is any point in having one.

All in all, I have been impressed by these newcomers in the SDS space and I can’t wait to play around with their gear at some point!

Filed Under: Software Defined, Storage, Virtual SAN Tagged With: , , , , ,

Designing your hardware for Virtual SAN

9 October, 2013 by 19 Comments

Over the past couple of weeks I have been watching the VMware VSAN Community Forum with close interest and also twitter. One thing that struck me was the type of hardware people used for to test VSAN on. In many cases this is the type of hardware one would use at home, for their desktop. Now I can see why that happens, I mean something new / shiny and cool is released and everyone wants to play around with it, but not everyone has the budget to buy the right components… And as long as that is for “play” only that is fine, but lately I have also noticed that people are looking at building an ultra cheap storage solution for production, but guess what?

Virtual SAN reliability, performance and overall experience is determined by the sum of the parts

You say what? Not shocking right, but something that you will need to keep in mind when designing a hardware / software platform. Simple things can impact your success, first and foremost check the HCL, and think about components like:

  • Disk controller
  • SSD / PCIe Flash
  • Network cards
  • Magnetic Disks

Some thoughts around this, for instance the disk controller. You could leverage a 3Gb/s on-board controller, but when attaching lets say 5 disks to it and a high performance SSD do you think it can still cope or would a 6Gb/s PCIe disk controller be a better option? Or even leverage 12Gb/s that some controllers offer for SAS drives? Not only can this make a difference in terms of number of IOps you can drive, it can also make a difference in terms of latency! On top of that, there will be a difference in reliability…

I guess the next component is the SSD / Flash device, this one is hopefully obvious to each of you. But don’t let these performance tests you see on Tom’s or Anandtech fool you, there is more to an SSD then just sheer IOps. For instance durability, how many writes per day for X years life can your SSD handle? Some of the enterprise grades can handle 10 full writes or more per day for 5 years. You cannot compare that with some of the consumer grade drives out there, which obviously will be cheaper but also will wear out a lot faster! You don’t want to find yourself replacing SSDs every year at random times.

Of course network cards are a consideration when it comes to VSAN. Why? Well because I/O will more than likely hit the network. Personally, I would rule out 1GbE… Or you would need to go for multiple cards and ports per server, but even then I think 10GbE is the better option here. Most 10GbE are of a decent quality, but make sure to check the HCL and any recommendations around configuration.

And last but not least magnetic disks… Quality should always come first here. I guess this goes for all of the components, I mean you are not buying an empty storage array either and fill it up with random components right? Think about what your requirements are. Do you need 10k / 15k RPM, or does 7.2k suffice? SAS vs SATA vs NL-SATA? Also, keep in mind that performance comes at a cost (capacity typically). Another thing to realize, high capacity drives are great for… yes adding capacity indeed, but keep in mind that when IO needs to come from disk, the number of IOps you can drive and your latency will be determined by these disks. So if you are planning on increasing the “stripe width” then it might also be useful to factor this in when deciding which disks you are going to use.

I guess to put it differently, if you are serious about your environment and want to run a production workload then make sure you use quality parts! Reliability, performance and ultimately your experience will be determined by these parts.

<edit> Forgot to mention this, but soon there will be “Virtual SAN” ready nodes… This will make your life a lot easier I would say.

</edit>

Filed Under: Server, Software Defined, Storage, Virtual SAN Tagged With: , , ,

VMware vSphere Virtual SAN design considerations…

9 September, 2013 by 10 Comments

I have been playing a lot with vSphere Virtual SAN (VSAN) in the last couple of months… I figured I would write down some of my thoughts around creating a hardware platform or constructing the virtual environment when it comes to VSAN. There are some recommended practices and there are some constraints, I aim to use this blog post to gather all of these Virtual SAN design considerations. Please read the VSAN introduction, how to install VSAN in your virtual lab and “How do you know where an object is located” to get a better understanding of the product.

The below is all based on vSphere 5.5 Virtual SAN (public) Beta and my interpretation and thoughts based on various conversations with colleagues, engineering and reading various documents.

  • vSphere Virtual SAN (VSAN) clusters are limited to a maximum total of 8 hosts and there is a minimum of 3 hosts. (Note that this is the limit for the beta, this will change over time!) VSAN is also currently limited to 100 VMs per host, resulting in a maximum of 800 VMs in an 8 host cluster.
  • It is recommended to use two 10GbE NICs for your VSAN VMkernel traffic, although 1GbE is fully supported it could be a limiting factor in I/O intensive environments. Both VSS and VDS are supported.
  • It is recommended to have a VSAN VMkernel on every physical NIC! Ensure to configure them in a “active/standby” configuration so that when you have 2 physical NIC ports and 2 VSAN VMkernel’s each of them will have its own port. Do note that multiple VSAN VMkernel NICs on a single host on the same subnet is not a supported configuration, in  different subnets it is supported.
  • IP Hash Load Balancing is supported by VSAN, but due to limited number of IP-addresses between source/destination load balancing benefits could be limited. In other words, an etherchannel formed out of 4x1GbE NIC will most likely not result in 4GbE.
  • Although Jumbo Frames are fully supported with VSAN they do add a level of operational complexity. When Jumbo Frames are enabled ensure these are enabled end-to-end!
  • VSAN requires at a minimum 1 SSD and 1 Magnetic Disk per diskgroup on a host which is contributing storage. Each diskgroup can have a maximum of 1 SSD and 6 magnetic disks. When you have more than 6 HDDs or two or more SSDs you will need to create an additional diskgroup.
  • Each host that is providing capacity to the VSAN datastore has at least one local diskgroup. There is a maximum of 5 disk groups per host!
  • Ensure when sizing your environment to take data replicas in to account. If your environment needs N+1 or N+2 resiliency factor this in accordingly.
  • SSD capacity does not count towards total VSAN datastore capacity. When sizing your environment, do not include SSD capacity in your totalized capacity calculation.
  • It is a recommended practice to have a minimum 1:10 ratio of SSD capacity to HDD capacity in each disk group. In other words, when you have 1TB of HDD capacity, it is recommended to have at least 100GB of SSD capacity.
  • By default, 70% of the available SSD capacity will be used as read cache and 30% will be used as a write buffer. As in most designs, when it comes to cache/buffer –> more = better.
  • Selecting the SSD with the right performance profile can make a 5x-10x difference in VSAN performance easily, chose carefully and wisely. Both SSD and PCIe flash solutions are supported, but there are requirements! Make sure to check the HCL before purchasing new hardware. My tip Intel S3700, great price/performance balance.
  • VSAN relies on VM Storage Policies for policy based management. There is a default policy under the hood, but you cannot see this within the UI. As such it is a recommended practice to create a new standard policy for your environment after VSAN has been configured. It is recommended to start with all settings set to default except for “Number of failures to tolerate” which should be configured to 1. This will ensure that when a single host fails virtual machines can be restarted and recovered from this failure with minimal impact on the environment. Attach this policy to your virtual machines when migrating them to VSAN or during virtual machine provisioning.
  • Configure vSphere HA isolation response to “power-off” to ensure that virtual machines which reside on an isolated host can be safely restarted.
  • Ensure vSphere HA admission control policy (“host failures to tolerate” or the “percentage based) aligns with your VSAN availability strategy. In other words, ensure that both compute and storage are configured using the same “N+x” availability approach.
  • When defining your VM Storage Policy avoid unnecessary usage of “flash read cache reservation”. VSAN has internal read cache optimization algorithms, trust it like you trust the “host scheduler” or DRS!
  • VSAN does not support virtual machine disks greater than 2TB, VMs which require larger VMDKs are not suitable candidates at this point in time for VSAN.
  • VSAN does not support FT, DPM, Storage DRS or Storage I/O Control. It should be noted though that VSAN internally takes care of scheduling and balancing when required. Storage DRS and SIOC are designed for SAN/NAS environments.
  • Although supported by VSAN, it is recommended practice to keep the hosts/disk configuration for a VSAN cluster similar. Non-uniform cluster configuration could lead to variations in performance and could make it more complex to stay compliant to defined policies after a failure.
  • When adding new SSDs or HDDs ensure these are not pre-formatted. Note that when VSAN is configured to “automatic mode” disks are added to existing disk groups or new disk groups are created automatically.
  • Note that vSphere HA behaves slightly different in a VSAN enabled cluster, here are some of the changes / caveats
    • Be aware that when HA is turned on in the cluster, FDM agent (HA) traffic goes over the VSAN network and not the Management Network. However, when an potential isolation is detected HA will ping the default gateway (or specified isolation address) using the Management Network.
    • When enabling VSAN ensure vSphere HA is disabled. You cannot enable VSAN when HA is already configured. Either configure VSAN during the creation of the cluster or disable vSphere HA temporarily when configuring VSAN.
    • When there are only VSAN datastores available within a cluster then Datastore Heartbeating is disabled. HA will never use a VSAN datastore for heartbeating.
    • When changes are made to the VSAN network it is required to re-configure vSphere HA.
  • VSAN requires a RAID Controller / HBA which supports passthrough mode or pseudo passthrough mode. Validate with your server vendor if the included disk controller has support for passthrough. An example of a passthrough mode controller which sells separately is the LSI SAS 9211-8i.
  • Ensure log files are stored externally to your ESXi hosts and VSAN by leveraging vSphere’s syslog capabilities. (added 23/09/2013)
  • In the beta release, always ensure to have “number of failures to tolerate” defined in your VM Storage Policy, when not defined the value will default to “0″ leading to no resiliency. (added 23/09/2013)

That is it for now. When more comes to mind I will add it to the list!

<change log>
initial post: 9th of September
Update 1: 10th of September
Update 2: 11th of September
Update 3: 23rd of September
</changelog>

Filed Under: Server, Software Defined, Storage, Virtual SAN Tagged With: , , , , , , ,

How do you know where an object is located with Virtual SAN?

5 September, 2013 by 7 Comments

You must have been wondering the same thing after reading the introduction to Virtual SAN. Last week at VMworld I received many questions on this topic, so I figured it was time for a quick blog post on this matter. How do you know where a storage object resides with Virtual SAN when you are striping across multiple disks and have multiple hosts for availability purposes, what about Virtual SAN object location? Yes I know this is difficult to grasp, even with just multiple hosts for resiliency where are things placed? The diagram gives an idea, but that is just from an availability perspective (in this example “failures to tolerate” is set to 1). If you have stripe width configured for 2 disks then imagine what could happen that picture. (Before I published this article, I spotted this excellent primer by Cormac on this exact topic…)

Luckily you can use the vSphere Web Client to figure out where objects are placed:

  • Go to your cluster object in the Web Client
  • Click “Monitor” and then “Virtual SAN”
  • Click “Virtual Disks”
  • Click your VM and select the object

The below screenshot depicts what you could potentially see. In this case the Policy was configured with “1 host failure to tolerate” and “disk striping set to 2″. I think the screenshot explains it pretty well, but lets go over it.

The “Type” column shows what it is, is it a “witness” (no data) or a “component” (data). The “Component state” shows you if it is available (active) or not at the moment. The “Host” column shows you on which host it currently resides and the “SSD Disk Name” column shows which SSD is used for read caching and write buffering. If you go to the right you can also see on which magnetic disk the data is stored in the column called  “Non-SSD Disk Name”.

Now in our example below you can see that “Hard disk 2″ is configured in RAID 1 and then immediately following with RAID 0. The “RAID 1″ refers to “availability” in this case aka “component failures” and the “RAID 0″ is all about disk striping. As we configured “component failures” to 1 we can see two copies of the data, and we said we would like to stripe across two disks for performance you see a “RAID 0″ underneath. Note that this is just an example to illustrate the concept, this is not a best practice or recommendation as that should be based on your requirements! Last but not least we see the “witness”, this is used in case of a failure of a host. If host 10.20.177.19 would fail or be isolated from the network somehow then the witness would be used by host 10.20.177.17 to claim ownership. Makes sense right?

Virtual SAN object location

Hope this helps understanding Virtual SAN object location a bit better… When I have the time available, I will try to dive a bit more in to the details of Storage Policy Based Management.

Filed Under: Server, Software Defined, Storage, Virtual SAN Tagged With: , , , , ,

Testing vSphere Virtual SAN in your virtual lab with vSphere 5.5

2 September, 2013 by 11 Comments

For those who want to start testing the beta of vSphere Virtual SAN in their lab with vSphere 5.5 I figured it would make sense to describe how I created my nested lab. (Do note that performance will be far from optimal) I am not going to describe how to install ESXi nested as there are a billion articles out there that describe how to do that.I suggest creating ESXi hosts with 3 disks each:

  • Disk 1 – 5GB
  • Disk 2 – 20GB
  • Disk 3 – 200GB

After you have installed ESXi and imported a vCenter Server Appliance (my preference for lab usage, so easy and fast to set up!) you add your ESXi hosts to your vCenter Server. Note to the vCenter Server NOT to a Cluster yet.

Login via SSH to each of your ESXi hosts and run the following commands:

  • esxcli storage nmp satp rule add –satp VMW_SATP_LOCAL –device mpx.vmhba2:C0:T0:L0 –option “enable_local enable_ssd”
  • esxcli storage nmp satp rule add –satp VMW_SATP_LOCAL –device mpx.vmhba3:C0:T0:L0 –option “enable_local”
  • esxcli storage core claiming reclaim -d mpx.vmhba2:C0:T0:L0
  • esxcli storage core claiming reclaim -d mpx.vmhba3:C0:T0:L0

These two commands ensure that the disks are seen as “local” disks by Virtual SAN and that the “20GB” disk is seen as an “SSD”, although it isn’t using an SSD. There is another option which might even be better, you can simply add a VMX setting to specify the disks are SSDs. Check William’s awesome blog post for the how to.

After running these two commands we will need to make sure the hosts are configured properly for Virtual SAN. First we will add them to our vCenter Server, but without adding them to a cluster! So just add them on a Datacenter level.

Now we will properly configure the host. We will need to create an additional VMkernel adapter, do this for each of the three hosts:

  1. Click on your host within the web client
  2. Click “Manage” -> “Networking” -> “VMkernel Adapters”
  3. Click the “Add host networking” icon
  4. Select “VMkernel Network Adapter”
  5. Select the correct vSwitch
  6. Provide an IP-Address and tick the “Virtual SAN” traffic tickbox!
  7. Next -> Next -> Finish

When this is configured for all three hosts, configure a cluster:

  1. Click your “Datacenter” object
  2. On the “Getting started” tab click “Create a cluster”
  3. Give the cluster a name and tick the “Turn On” tickbox for Virtual SAN
  4. Also enable HA and DRS if required

Now you should be able to move your hosts in to the cluster. With the Web Client for vSphere 5.5 you can simply drag and drop the hosts one by one in to the cluster. VSAN will now be automatically configured for these hosts… Nice right. When all configuration tasks are completed just click on your Cluster object and then “Manage” -> “Settings” -> “Virtual SAN”. Now you should see the amount of hosts part of the VSAN cluster, number of SSDs and number of data disks.

Now before you get started there is one thing you will need to do, and that is enable “VM Storage Policies” on your cluster / hosts. You can do this via the Web Client as follows:

  • Click the “home” icon
  • Click “VM Storage Policies”
  • Click the little policy icon with the green checkmark, second from the left
  • Select your cluster and click “Enable” and then close

Now note that you have enabled VM Storage Policies, there are no pre-defined policies. Yes there is a “default policy”, but you can only see that on the command line. For those interested just open up an SSH session and run the following command:

~ # esxcli vsan policy getdefault
Policy Class Policy Value
------------ --------------------------------------------------------
cluster (("hostFailuresToTolerate" i1) ("forceProvisioning" i1))
vdisk (("hostFailuresToTolerate" i1) ("forceProvisioning" i1))
vmnamespace (("hostFailuresToTolerate" i1) ("forceProvisioning" i1))
vmswap (("hostFailuresToTolerate" i1) ("forceProvisioning" i1))
~ #

Now this means that in the case of “hostFailuresToTolerate”, Virtual SAN can tolerate a 1 host failure before you potentially lose data. In other words, in a 3 node cluster you will have 2 copies of your data and a witness. Now if you would like to have N+2 resilience instead of N+1 it is fairly straight forward. You do the following:

  • Click the “home” icon
  • Click “VM Storage Policies”
  • Click the “New VM Storage Policy” icon
  • Give it a name, I used “N+2 resiliency” and click “Next”
  • Click “Next” on Rule-Sets and select a vendor, which will be “vSan”
  • Now click <add capability> and select “Number of failures to tolerate” and set it to 2 and click “Next”
  • Click “Next” -> “Finish”

That is it for creating a new profile. Of course you can make these as complex as you want, their are various other options like “Number of disk stripes” and “Flash read cache reservation %”. For now I wouldn’t recommend tweaking these too much unless you absolutely understand the impact of changing these.

In order to use the profile you will go to an existing virtual machine and you right click it and do the following:

  • Click “All vCenter Actions”
  • Click “VM Storage Service Policies”
  • Click “Manage VM Storage Policies”
  • Select the appropriate policy on “Home VM Storage Policy” and do not forget to hit the “Apply to disks” button
  • Click OK

Now the new policy will be applied to your virtual machine and its disk objects! Also while deploying a new virtual machine you can in the provisioning workflow immediately select the correct policy so that it is deployed in a correct fashion.

These are some of the basics for testing VSAN in a virtual environment… now register and get ready to play!

Filed Under: Server, Software Defined, Storage, Virtual SAN Tagged With: , , , , ,

Introduction to VMware vSphere Virtual SAN

26 August, 2013 by 33 Comments

Many of you have seen the announcements by now and I am guessing that you are as excited as I am about the announcement of the public beta of Virtual SAN with vSphere 5.5. What is Virtual SAN, formerly known as “VSAN” or “vCloud Distributed Storage” all about?

Virtual SAN (VSAN from now on in this article) is a software based distributed storage solution which is built directly in the hypervisor. No this is not a virtual appliance like many of the other solutions out there, this sits indeed right inside your ESXi layer. VSAN is about simplicity, and when I say simple I do mean simple. Want to play around with VSAN? Create a VMkernel NIC for VSAN and enable it on a cluster level. Yes that is it!

vSphere Virtual SAN

Before we will get a bit more in to the weeds, what are the benefits of a solution like VSAN? What are the key selling points?

  • Software defined – Use industry standard hardware, as long as it is on the HCL you are good to go!
  • Flexible – Scale as needed and when needed. Just add more disks or add more hosts, yes both scale-up and scale-out are possible.
  • Simple – Ridiculously easy to manage! Ever tried implementing or managing some of the storage solutions out there? If you did, you know what I am getting at!
  • Automated – Per virtual machine policy based management. Yes, virtual machine level granularity. No more policies defined on a per LUN/Datastore level, but at the level where you want it to be!
  • Converged – It allows you to create dense / building block style solutions!

Okay that sounds great right, but where does that fit in? What are the use-cases for VSAN when it is released?

  • Virtual desktops
    • Scale out model, using predictive (performance etc) repeatable infrastructure blocks lowers costs and simplifies operations
  • Test & Dev
    • Avoids acquisition of expensive storage (lowers TCO), fast time to provision
  • Big Data
    • Scale out model with high bandwidth capabilities
  • Disaster recovery target
    • Cheap DR solution, enabled through a feature like vSphere Replication that allows you to replicate to any storage platform

So lets get a bit more technical, just a bit as this is an introduction right…

When VSAN is enabled a single shared datastore is presented to all hosts which are part of the VSAN enabled cluster. Typically all hosts will contribute performance (SSD) and capacity (magnetic disks) to this shared datastore. This means that when your cluster grows, your datastore will grow with it. (Not a requirement, there can be hosts in the cluster which just consume the datastore!) Note that there are some requirements for hosts which want to contribute storage. Each host will require at least one SSD and one magnetic disk. Also good to know is that with this beta release the limit on a VSAN enabled cluster is 8 hosts. (Total cluster size 8 hosts, including hosts not contributing storage to your VSAN datastore.)

As expected, VSAN heavily relies on SSD for performance. Every write I/O will go to SSD first, and eventually they will go to magnetic disks (SATA). As mentioned, you can set policies on a per virtual machine level. This will also dictate for instance what percentage of your read I/O you can expect to come from SSD. On top of that you can use these policies to define availability of your virtual machines. Yes you read that right, you can have different availability policies for virtual machines sitting on the same datastore. For resiliency “objects” will be replicated across multiple hosts, how many hosts/disks will thus depend on the profile.

VSAN does not require a local RAID set, just a bunch of local disks. Now, whether you defined a 1 host failure to tolerate ,or for instance a 3 host failure to tolerate, VSAN will ensure enough replicas of your objects are created. Is this awesome or what? So lets take a simple example to illustrate that. We have configured a 1 host failure and create a new virtual disk. This means that VSAN will create 2 identical objects and a witness. The witness is there just in case something happens to your cluster and to help you decide who will take control in case of a failure, the witness is not a copy of your object let that be clear! Note, that the amount of hosts in your cluster could potentially limit the amount of “host failures to tolerate”. In other words, in a 3 node cluster you can not create an object that is configured with 2 “host failures to tolerate”. Difficult to visualize? Well this is what it would look like on a high level for a virtual disk which tolerates 1 host failure:

With all this replication going on, are there requirements for networking? At a minimum VSAN will require a dedicated 1Gbps NIC port. Of course it is needless to say that 10Gbps would be preferred with solutions like these, and you should always have an additional NIC port available for resiliency purposes. There is no requirement from a virtual switch perspective, you can use either the Distributed Switch or the plain old vSwitch, both will work fine.

To conclude, vSphere Virtual SAN aka VSAN is a brand new hypervisor based distributed platform that enables convergence of compute and storage resources. It provides virtual machine level granularity through policy based management. It allows you to control availability and performance in a way I have never seen it before, simple and efficient. I am hoping that everyone will be pounding away on the public beta, sign up today: http://www.vmware.com/vsan-beta-register!

Filed Under: Server, Software Defined, Storage, Virtual SAN Tagged With: , , , , ,
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