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vmware view snapshot and replica

Posted on 2016-10-26
Medium Priority
Last Modified: 2016-10-30
In vmware view terminology, they use the term Replica. well I am not referring to Replica server.
If I understand when you go about configuring Linked clone, you will have  first to :
Prepare the Master image , for instance windows 7.
Turn the VM off
Take snapshot of it
Add a Pool , this will take you through a wizard, where you browse to the snapshot and Master image..and follow the wizard.
I do not see where the replica comes into play.
I just wonder  when they say replica if they refer to Master Image.

Any clarification ?

Thank you
Question by:jskfan
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LVL 123
ID: 41861633
Your are correct, in how you setup the Linked Clones.

They use the term replica, because that is the object which is replicated many times, e.g. to produce the VMs in the Pool.

and you will see these objects in the inventory, marked as replica.

Finding and removing unused replica virtual machines in the VMware Horizon View (2009844)

The Thin Clone (Master image object) is called the replica.

Author Comment

ID: 41862004
- So when the end point device connects to the connection server, this will create new VM off the Master Image(replica) or off  the Snapshot that has been taken off the Master image at the first place ?

- When do Entitlements come into play? the reason I am asking this question is that I have seen an environment where the user starts the end point device, this will either create new VM on Vsphere or use an existing VM.  
it sounds like any users who can start the end point device can generate new VM or use existing VM and probably even can get into he system, since some can have Autologin setup
LVL 123
ID: 41862007
- So when the end point device connects to the connection server, this will create new VM off the Master Image(replica) or off  the Snapshot that has been taken off the Master image at the first place ?

Yes and No, it depends on what settings you have defined in the pool, to Provision at Creation of Pool, or as Clients need the VDI.

Again, later in your question depends on how the pool has been configured. Some pools provision upfront to reduce the delay in a client/user waiting for a VM to spin up and be created.

Now with the provision of SSD/Flash, All Flash Arrays, provisioning speed has been reduced considerably.
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Author Comment

ID: 41865161
Again, later in your question depends on how the pool has been configured. Some pools provision upfront to reduce the delay in a client/user waiting for a VM to spin up and be created.
in either case, from which source the new VM is created ? from the Master image or from the snapshot(initially created off the Master image) ?
LVL 123
ID: 41865189
It's actually created from the Snapshot which is Linked Cloned to the Replica/Master,

So the Parent Disk (Master) with the Snapshot (Replica) = VDI Machine which end user uses.

Author Comment

ID: 41865281
he Parent Disk (Master) with the Snapshot (Replica) = VDI Machine which end user uses
Wait..wait Andrew.. confusion here

when you have VM(Master image), you turn it off and you create Snapshot.
The snapshot is just Delta file with nothing in it in the Beginning

So when End user connects to  the Pool, Vmware will create an identical VM (Master Image) to end user. (if it is not already created up front)
I do not see when the snapshot will be used unless you update the Master image
LVL 123
ID: 41865301
Master Image ---> Replica -----> Linked Clones

The Linked Clone is what the User connects to, which is a Thin clone, with blank snapshot, which gets written to in use.

Master Image is not touched or changed, because that happens in the Snapshot, you create and present and select with Composer, which generates the replica, which is linked cloned many times to create the VMs for Clients.

Author Comment

ID: 41865349
You have Master Image VM (MImage1), from which you create the snapshot the first time (Snapshot1).

User1 connects to Snapshot1 and write to it (Snapshot1 becomes the VM for User1)
User2 will connect then what happens ?
LVL 123
ID: 41865362
No, that's not correct.

A replica is created with a linked clone.

The User connects to a unique linked clone, which also has a snapshot attached., user2 connects to another linked clone, which has a snapshot.

Author Comment

ID: 41865380
Can you give a picture on how these pieces get created ?

I know that there is Master Image (which is initial VM), you turn it off and create Snapshot.
down there I am not sure how new VMs got created

Author Comment

ID: 41865389
Probably when you create a Pool and go through the wizard and point to the Master Image, VMware view will create a clone of the Master image (which is called Replica)

Author Comment

ID: 41865390
and probably at the same time, Vmware will create snapshot for each replica
LVL 123
ID: 41865401
good screenshots here


Author Comment

ID: 41865810
I looked at that link and also this link, as it is with newer version:
on the top page it stated "Based on that snapshot a Replica virtual machine will be created as part of the pool creation"
 half way down it stated " Linked-clones are made by a snapshot of the golden image"

Well, if a Replica is made of Snapshot, then there should be nothing in it
the same applies to Linked Clones, if they are made of snapshot then there is nothing in there.

The bottom line when end user starts up the VDI, it should connect to a VM, that runs an OS , just like logging to physical computer,
so where does that OS come from? since the Master Image is powered off and the snapshot is just an empty file, and anything created from that snapshot (as they stated: Replica and Linked clones) should also be empty file.
LVL 123
ID: 41865822
That page is not quite correct, the first statement is correct that a replica is made, and a new VM is made, but a link clone is created, rather than a Full Clone. e.g. the parent virtual machine disk is read only, and all writes are too a snapshot. - this reduces space.

it's a Linked Clone to the Replica, with Snapshot being written to by the user.

As you have stated, the Master Image is OFF.

Again my simple diagram

Master Image  (OFF) --> Replica (ON) -----> Linked Clones (ON)

Have you ever experimented with Linked Clones ? and NOT in a VDI environment, e.g. VMware Workstation, where you can create a VM, but Link Clone it to a Parent VM

Author Comment

ID: 41865827
I created a LAB long time ago.... but when you use a LAB you do not pay attention how things work in the background...I mean how Things are cooked until users get that VM provisoned to them.

That's what I am trying to understand..How things are tied up..

OK..we all know that you need Master Image, Turn it off then create snapshot off it.
Add pool and point to the Master Image and Snapshot you have previously created..
Then what happens till user can see a desktop just like they are logging to a physical computer ?
LVL 123
ID: 41865853
Pool is created, VM (VDI machines) are spun up and, Sysprepped, Joined to Domain e.g. Linked Clones

Agent in the VM starts, registered with the Pool,

Client connects to Connection Server and gets allocated and logs into the VM

Changes are committed to the Snapshot of VM Linked Clone, because the Parent Replica is read only.

Author Comment

ID: 41865964
I followed this video example... I know it is hard to take stop and take screenshots of the video properly
well on this video, I am not if the author is creating 2 VMs or just one.

I followed the task on the bottom of Vsphere client page. I noticed the following steps:
-View folder has been created
-clone of the Parent VM (Master Image) has been created
-VM snapshot has been created
-Add Tag
-Clone VM (Replica)
- Add Tag
-Reconfigure VM


Author Comment

ID: 41865977
LVL 123
ID: 41866004
and the question is ?

the last task is creating the Linked Clone, it's a clone of the replica, BUT a linked clone, and not a full clone.

Author Comment

ID: 41866119
What I want to make sure I understood is:

The Replica is 100% photocopy of the Parent VM

when user1 connects , it will connect to the Replica , and the replica will spit out a new snapshot for user to write on ,
when user2  connects (is Vmware going to create a new Replica2 and new snapshot2 ?)
and each user who connects , a new Replica will be created and also new snapshot will be created ?
LVL 123

Accepted Solution

Andrew Hancock (VMware vExpert / EE MVE^2) earned 2000 total points
ID: 41866179
The Replica is 100% photocopy of the Parent VM


The user connects to "Replica"+"Snapshot" = "Linked Clone."

So in the inventory, there is an actual Linked Clone object virtual machine, which the user connects to, which is generated from replica+snapshot.

Users do not connect to replica, it's used with the snapshot, to create a new VM object. Hence when the pool is created you will see x number of virtual machines created in the inventory, these are the VMs, users connect to which has the agent in.

These are Linked Clones. if a Linked Clone Pool is created, if you did not use Linked Clones, they would be a Full Clone with no snapshot.

A new Replica is not necessarily created, because one replica object can support many snapshots = Linked Clone.

Clients connect to the Linked Clone which is made up of Writeable Snapshot + Replica Object (which is a CLONE of the Parent VMDK (Master Image))

This is probably going to blow you head off, but a single replica object can support up to 4,000 VMs (VMs, VDI machines, clients, users whatever you want to call them), so yes that's also 4,000 snapshots all linked back to a single object!

Now you can see why tiered storage is required, and recommended that use use SSD, Flash Arrays or View.

I would encourage you to look at Linked Clones in the Lab (not necessarily VDI), and create 20 Linked Clones from a Single Server Windows 2012 server, yes you can have Linked Clones from a Windows 2012 server, all using snapshots to write to...as an experiment, it's not supported for production, but you'll begin to see the possibilities, of reducing storage even further using Linked Clones.

So that's a single Parent VMDK and then 20 VMs all powered up just using the space of the parent + snapshot, rather than A 40GB Server x 21, you can have 1 server using 40GB, and 20 snapshots....to reduce storage.

Author Comment

ID: 41866241
That's clear enough Andrew
Thank you very much!
LVL 123
ID: 41866258
no problems

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