Linked Clones

It depends   But to help you better guesstimate how much storage you’ll save with View Composer, let’s take a look at the actual storage savings in my home lab.  Keep in mind that VMware View isn’t just something I’m playing around with.  There are currenlty 5 other VMware Systems Engineers using my lab on a regular basis.  And I use VMware View to give each lab user a dedicated, persistent desktop VM which they connect to remotely via the View Client.  And from their dedicated lab desktop, they have full access to the lab environment I’ve built.  So, while my home lab environment may be small and by no means a production enviornment, I’m still using VMware View as a “production” application, so to speak.  It’s the one application in my lab that needs to be up, and it gets heavily used.

Let’s first look at how much storage my virtual desktop infrastructure would require without the use of View Composer.  As I said, each lab user has a dedicated desktop, which has a 12G partition for OS and a 4G partition for user data.  Also, each desktop has 1G of memory with zero memory reservation, which transltates into a 1G swap file.  That’s a total of 17G per user.  Right now there are 5 other remote users, plus I have a desktop for myself.  And I have 2 desktops on standby for new users (so they don’t have to wait for a new VM to be built upon first login).  So, that brings the total virtual desktops to 8.  Therefore the total storage requirement for virtual desktops in my lab without View Composer would be 136G (17G * 8 desktops).

Now let’s look and see how much space is actually being used in my lab.  Here’s a cut and paste showing the disk usage of the volume holding the desktop VMs …

[root@cincylab-esx1 cincylab-vol1]# du -sh *
3.1G    labuser-01
2.9G    labuser-02
3.6G    labuser-03
2.6G    labuser-04
3.1G    labuser-05
1.9G    labuser-06
1.5G    labuser-07
1.5G    labuser-08
2.0G    replica-774c678b-e6b5-495a-b8ff-
448K    source-lc-8ae5400e-4af3-4a09-8d8
13G     parent_desktop
[root@cincylab-esx1 cincylab-vol1]#

The grand total here is 33.2G, which is about a 75% reduction in storage.  Not bad.  The storage reduction is achieved through two technologies, Linked Clones and Thin Disks.

Linked Clones

In my environment, the virtual disks for the desktops are located in the labuser-0* directories (this is done automatically for me during the deployment process).  These virtual disks are not thick, monolithic disks like they used to be in the previous version.  Rather, they are delta disks, which only store data differences between the desktop OS and the OS of the parent VM.  In the cut and paste above, notice the 13G parent_desktop?  That’s my starting point and contains my golden image.  That direcotry also contains a snapshot,  which I took when I was ready to being deploying desktops.  The replica-774c678b-e6b5-495a-b8ff- VM is derived from this snapshot and ultimately serves as the parent VM (for now, this can change over time) of the labuser-0* desktops.  Linked Clones have other benefits too, especially around patching and updateing.  But that’s a topic for a later post.

Thin Disks

Remember how I said the users need a 17G? (12G for OS, 4G for user data and 1G for swap)  But did you notice that the parent_desktop directory is only 13G in size (12G OS plus 1G swap)?  From the administration guide “Thin provisioned disks (thin disks) are used by the linked clones to store user data, and are not linked to the Parent VM.”  So I didn’t need to include the user partition in the parent VM.  The user partition is handled for me when a desktop is deployed and included with each of the user desktops.  User data disks are persistent and they are thin, meaning they occupy no more space than the data requires.  In my environment, looking at the virtual disks for labuser-03:

[root@cincylab-esx1 labuser-03]# ls -lah
total 3.6G
drwxr-xr-x    1 root     root         1.8K Dec 27 09:23 .
drwxr-xr-t    1 root     root         3.7K Jan  5 06:10 ..
-rw——-    1 root     root         1.0G Dec 27 09:23 labuser-03-a2263868.vswp
-rw——-    1 root     root         8.5K Dec 27 09:23 labuser-03.nvram
-rw——-    1 root     root         4.0G Jan  5 08:07 labuser-03-vdm-user-disk-D-flat.vmdk
-rw——-    1 root     root          443 Dec 27 09:24 labuser-03-vdm-user-disk-D.vmdk
-rw——-    1 root     root           75 Dec 27 09:21 labuser-03.vmsd
-rwxr-xr-x    1 root     root         3.9K Dec 31 06:58 labuser-03.vmx
-rw——-    1 root     root          265 Dec 31 06:58 labuser-03.vmxf
-rw——-    1 root     root         2.5G Jan  5 08:07 replica-774c678b-e6b5-495a-b8ff–cl1-delta.vmdk
-rw——-    1 root     root          379 Dec 27 09:24 replica-774c678b-e6b5-495a-b8ff–cl1.vmdk
-rw-r–r–    1 root     root          62K Dec 27 09:21 vmware-1.log
-rw-r–r–    1 root     root          36K Jan  5 06:21 vmware.log
[root@cincylab-esx1 labuser-03]#

Look at the size of labuser-03-vdm-user-disk-D-flat.vmdk, see how the file system “thinks” it’s 4.0G?  It’s really not.  A closer look at disk usage reaveals:

[root@cincylab-esx1 labuser-03]# du -sh *
1.0G    labuser-03-a2263868.vswp
64K     labuser-03.nvram
43M     labuser-03-vdm-user-disk-D-flat.vmdk
64K     labuser-03-vdm-user-disk-D.vmdk
64K     labuser-03.vmsd
64K     labuser-03.vmx
64K     labuser-03.vmxf
2.6G    replica-774c678b-e6b5-495a-b8ff–cl1-delta.vmdk
64K     replica-774c678b-e6b5-495a-b8ff–cl1.vmdk
64K     vmware-1.log
64K     vmware.log
[root@cincylab-esx1 labuser-03]#

It’s actually only taking up 43M, not 4G.  And a quick look inside the VM confirms it too “thinks” it has 4G:

So that’s my real world example of how much storage I’m saving with View Composer.  How much will you save?  Again, it depends   There are things that I haven’t discussed in this post (e.g. desktop refresh, desktop recomposition and desktop rebalance), which will also affect storage savings.  Also, using ThinApp’d applications that live on a file share (as opposed to putting them in the OS) could have a big positive impact on storage savings.  In my lab, with only linked clones and thin disks, I’m getting a 75% reduction.  With a little more effort and planning on my part, I’m confident I could achieve 85% or better.