VMware vSAN Advanced Concepts – 2

In continuation from the previous post lets discuss the remaining advanced concepts of VMware vSAN, This post will cover Diskgroups types both All-flash architecture and Hybrid architecture, vSAN Datastore and its format, vSAN Objects and vSAN Components and Upgrading Virtual SAN.

Diskgroup Types

We must design the environment depending upon the requirement. From vSAN 6 onwards we can choose All flash if we are going to run mission critical highly available workloads that are very high IO intensive. Else we can also choose to go with Hybrid type which will also provide good performance for Tier -1 production workloads. Below picture illustrates how both the Diskgroup types match up.


All Flash configurations guarantees uniform performance regardless of the workload that we are running as compared to Hybrid configurations. Only All Flash configuration supports some advance features such as RAID 5/RAID 6 , Compression and Deduplication as well. There are two types of All Flash configurations very fast, durable and expensive SSD for Cache, and more capacity and write intensive, cost effective less fast capacity SSD. We must consider the following before going ahead with All Flash design
1) All Flash is only available after vSAN 6 release
2) RAID 5/6, Compression and Deduplication available only in Advanced and Enterprise license
3) A minimum of 10Gb network bandwidth and 1Gb network is not supported
4)  All Flash configuration uses 100% cache only for writes and no Flash Read Cache Storage policy is used here

Hybrid configuration clusters use both magnetic disks for capacity and flash disks for cache. We must design the cache to be a minimum of 10% of our Total Usable Capacity in our design. However in Hybrid configuration 70% of cache is used for frequently Read data and 30% for write buffer. In a Hybrid configuration we must use a minimum of one SSD and maximum of seven magnetic drives for every Diskgroup.

vSAN Datastore

vSAN is an Object Store that is represented to vSphere Hosts as vSphere file system or VMFS Datastore. Object Store mounts all the volumes that is presented to it while we created the Diskgroups. vSAN represents all the Diskgroups in one single vSAN Datastore. In vSAN 6 there has been an update on the Disk Format from VMFS-L to Virtual SAN FS which in turn brings a host of improvements in Performance, Scalability and Migration capabilities in vSAN. However an upgrade from existing VMFS-L is just optional. All the contents in vSAN is represented as Objects and Components which will be discussed below.

Virtual SAN Objects

Virtual SAN manages data in the form of data containers called as Objects. Typical virtual machine files are referred to as Objects. There are 5 types of virtual machine Objects :
1) Virtual Machine Directory (VM Home)
2) Virtual Machine Swap file (vswp)
3) Virtual Machine Snapshots (vmsd/vmsn)
4) Virtual Machine Memory (vmem)
5) VMDK file
These Objects are further broken down in to smaller data containers depending upon the storage policies called Components

Virtual SAN Components

Virtual SAN components are chunks of objects that are distributed in multiple ESXi Hosts to satisfy storage policies such as FTT and others. By default if any objects exceeds 256 GB then it is automatically broken down to multiple Components. Components are spread across multiple Hosts using RAID 0 and RAID 1 techniques. A maximum of 9000 Components can be managed by each ESXi Host.

Upgrading vSAN

Upgrading vSAN Cluster is more just a vSphere Upgrade. We can classify the upgrade activity into two different phases :

Phase 1 : Upgrade to vSphere 6 or Fresh Installation of vSphere 6
1) vCenter Server upgrade from 5.5 to 6.x using any method
2) ESXi Hypervisor upgrade from 5.5 to 6.x using VUM, Simple Install or CLI

Maintenance Mode generally using Ensure Accessibility

Phase 2 :

Prerequisites that needs to be satisfied before phase 2 :
1) vCenter Server upgraded to 6
2) All the Hosts in cluster upgraded to 6
3) Disk Cliam rule in the Disk group set to “Manual”

Only after the above prerequisites are fulfilled we can proceed to phas 2 upgrade which includes

1) Disk Group upgrade
2) Object upgrade

Here all the data from the disk group is evacuated and the disk group is reformated to V2 mode from V1 mode.
Once disk group becomes available again all Objects are now placed on V2 mode but Objects themselves are still in V2 mode.
We must now convert Objects also to V2 mode and this brings back all the vSAN 6 features to the diskgroup.

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