There are new videos of VSAN available through VMwareTV YouTube Channel. There are 5 of them and all showing VSAN, the configuration steps and availability. Precisely one of those videos (video 5) which shows the details what happens if there is a host failure and the VM storage policy has been defined with Number of failures to tolerate = 1 and additional stripe width.
Number of Failures to tolerate – how many number of hosts, network and/or disk failures a storage object can tolerate. Example for N number of failures to be tolerated in the cluster, “N+1″ copies of the storage object (VMs files) are created and at least “2N+1″ hosts are required to be in the cluster
In that particular video we will see a single host failure. What happens? The Virtual machine keeps running, because the virtutal machine files are spread between two hosts in RAID 1 configuration. (defined via the VM storage policy). Note that 3 hosts is a minimum requirements for VSAN configuration as the third hosts is with a “Witness” disk is used as a judge in “split brain” scenarios.
This is quite new scenarios which will be introduced to vSphere cluster design. Quite different what we know on usual design scenarios of HA cluster with classic shared storage, SAN or NAS based. Note that the VSAN 1.0 cluster size has 8 host limit (soft limit of the Beta). Check more limits in this post.
With VMware VSAN It's much easier to provision another host and expand the VSAN cluster from the storage (compute, memory) point of view. Adding another host with local disks automatically expands the VSAN cluster. VMware VSAN requirements and details were outlined in my post VMware VSAN introduced in vSphere 5.5 – How it works and what’s the requirements?.
VMware vSphere 5.5 brings some huge number of improvements and doubles the configuration maximums. But I think that we all use to it and we kind of become blazed with that since VMworld Copenhagen in 2011 where Monster VMs first appeared. Check out my VMware vSphere 5.5 page with the latest detailed articles which I published so far.
Here are the links and explanations for each of those videos which has been officially recorded by VMware. I usually watch them several times with HD and fullscreen to get the details.
Virtual SAN (VSAN) Setup 
– It's 2 steps process. You'll see how to add hosts to VSAN cluster, by creating new VMkernel network adapter and activating VSAN traffic service. Then by creating a disk groups (auto or manual way) by picking two disks at least from each host. You need at least 1 HDD in a disk group. Note that host without DAS storage (not participating in VSAN cluster) can still be part of the VSAN cluster and connect to the shared VSAN datastore.- Deploying a Virtual Machine on Virtual SAN (VSAN) – By creating and using VM storage policies (automatically enabled after creating VSAN cluster), which are “showed up” by VASA. By adding a “capability” you define the storage policy. As a capabilities, you can chose from Number of disk stripes per object (RAID 0) , Flash read cache reservation (%) – ( distributes space evenly between VMs by default), Number of failures to tolerate (RAID 1), Force provisioning (provisions VM even if there is not enough resources in the underlying storage) and Object space reservation (%).
Virtual SAN (VSAN) Setup
Changing a VM Storage Policy On-The-Fly with VSAN – this video shows when changing the storage policy with VM running. From RAID 1 they change to include an additional stripe width for IO intensive applications. They do RAID 10. The VMs disks are copied to additional stripes while the VM is running. Quite cool. It's possible by adding additional capability to existing rule. In this case to existing Number of failures to tolerate (raid1) they've added number of disk stripes per object. (set to 2). While validating you got an option to apply manually later or apply imediately.
- Virtual SAN (VSAN) & vSphere HA Interoperability – VMware HA can restart VMs on other hosts in a VSAN cluster even if there is no traditional shared storage. VSAN and HA interoperate. You'll see HA being activated and setup to tolerate 1 host failure. VMs running on failed host are restarted on other hosts of the VSAN cluster.
- Virtual SAN (VSAN) & VM Availability – This is the video I've been talking about at the beginning of my article. It shows what happens when one of your host which is part of the VSAN cluster, goes down. What happens to a VM which runs on that host…. The VM stays alive.. -:)
Source: VMwareTV YouTube Channel
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