farhadkh000
Contributor
Contributor

how vsan choicing the best place for objects ?

hi i am farhad
i need to understand,
how vsan choicing the best place for objects ?
for example , in my cluster drs is enabled , when i created a vm , drs choiceed best host for vm but in disks of that host no space for objects ,now What is the decision for distribut object in vsandatastor ?
Does vsan have a specific plan for this?
and after many time that host released capacity in disk so it is possible that objects moved on this host ? ( The host on which the virtual machine compute are)

Or in another example
i have one host with cpu and memory low level of another hosts in cluster not about disk group ( disk group in all host is the same )
Is there a requirement for objects to be placed on the host that is responsible for computing virtual machins?

Is it possible to be selected by drs Host x due to having a better resource for computing even when this is possible in y Host for creat vm ? but virtual machine objects are created in y Host which has free space in its disks

Is there anything in vsan as the primary object? Where can it be found? if primary object fail ,how vsan choice the next primary?
Thank you for your help

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4 Replies
depping
Leadership
Leadership

Hi, most of your questions are described in either documentation (docs.vmware.com and core.vmware.com/vsan) or one of the many blog posts posted by either myself (yellow-bricks.com) or Cormac Hogan (cormachogan.com)

Anyway:

  1. VM Compute and VM storage objects do not need to be aligned
  2. VMs, from a compute stance, can move around freely
  3. There's no such thing as "primary" or "active" with vSAN
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farhadkh000
Contributor
Contributor

Thank you very much for your help👍
I have used the content of both sites before, they have very useful and good content.
So DRS can move the vm compute anywhere without any obligation(Based on need and the best choice).

Now if I need to filter a host (in terms of ram, cpu usage) and use only host disks, is there a solution?

How can I do this in vcenter?

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depping
Leadership
Leadership

Yes, the VM can move to any host in the cluster,  it doesn't matter where the storage of the VM is located. DRS doesn't take vSAN in account at all.

"Now if I need to filter a host (in terms of ram, cpu usage) and use only host disks, is there a solution? How can I do this in vcenter?

Not sure what that means? 

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TheBobkin
VMware Employee
VMware Employee

@farhadkh000 ,(tried posting this a few days ago but account was locking me out -_-)

DRS doesn't determine where data-components of Objects are placed, DRS only determines/advises where the compute resources of the VM will reside and this has no bearing on where the data-components will be (e.g. a vmdk could have data components on nodes 1, 2 and 3 but be running on node 4).
vSAN determines component placement based on 1. where are applicable locations that won't violate the rules of the Storage Policy (e.g. site-affinity or multiple components of both data replicas of an Object on a single node) and 2. where (that doesn't violate the Storage Policy rules) has the most free space.
Components only get moved (technically re-created) for reasons such as rebalances (either proactive or automatic based on clom rebalance threshold), hosts being placed into maintenance mode (e.g. with full-data migration option), components being repaired due to a replica being gone (either right away due to a failure or later if due to clom repair delay timer expiring).
There is no such thing as 'primary objects' - RAID1 data is stored as synchronously replicated mirrors of each other and one is not 'primary' or better than the other as they are equals, that being said (likely only if the cluster is under heavy load already) a VM might perform slightly better if the DOM-Owner of an Object is the node it is running on (but again, this would only be for that vmdk Object and this doesn't mean the same node is the DOM-Owner of any other Objects that belong to that VM or new ones e.g. snapshots).