Yellow Bricks

by Duncan Epping

snapshots

Where’s my vSAN Data Protection screen in 8.0 U3?

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The first time I deployed vSphere/vSAN 8.0 U3 I immediately looked for the vSAN Data Protection UI. I always get excited about new features, and simply want to test it. I mean who doesn’t like scalable snapshots and a great way of managing snapshot schedules? Finally available within the vSphere Client! Of course, I could not find it, but I figured that was because I was on some weird alpha build of the product. Now that the product has shipped it must be there out of the box right?

No it isn’t. You will need to deploy an appliance in order for this functionality to appear in the UI. The appliance can be found under “Drivers and Tools” under the vSphere Hypervisor download (Which is under VMware vSphere), it is called “VMware vSAN Snapshot Service Appliance”. The current version is named “snapservice_appliance-8.0.3.0-24057802_OVF10.ova”. You need to deploy this OVA, and I would highly recommend to request a DNS name for it and have it properly registered. I fiddled around with the hosts file on VCSA and forgot to add the name to my local host file on my laptop and had some weird issues as a result, which I am trying to reproduce at the moment, will report back if/when I can.

The other thing to point out is the following, the documentation tells you to download the certs and copy the text for the Appliance, it isn’t something most of us do daily either, you can simply open a web browser and use the following url “https://<name of your vCenter server>/certs/download.zip” to download the certs and then unzip the downloaded file. (More details to be found here.) It will contain the certs, and if you open the cert with a proper text editor you can copy/paste that into the deployment screen for the OVA. (Yes, I know there are other ways as well, but I found this one to be the easiest.)

Now when you deployed the OVA, and when everything was configured correctly you should see a successful task, or actually two: download plugin, deploy plug, as shown in the next screenshot.

If you do get the “error downloading plug-in” error message, it likely is one of two things:

  1. DNS / Hosts files are not correctly configured, resulting in the URL not being reachable. Make sure you can resolve the URL!
  2. Cert thumbprint was incorrectly copied/pasted, there’s a whole section on troubleshooting this here.

Okay, now that I got the appliance up and running, I will probably do a follow-up post on what you can do with it 🙂

Changes to Snapshot mechanism “Delete All”

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Don’t know if anyone noticed it or not but with the latest set of patches VMware changed the “Delete All” mechanism that is part of the Snapshot feature. I wrote multiple articles about the “Delete All” functionality as it often led to completely filled up VMFS volumes when someone used without knowing the inner workings.

Source

When using the Delete All option in Snapshot Manager, the snapshot farthest from the base disk is committed to its parent, causing that parent snapshot to grow. When the commit is complete, that snapshot is removed and the process starts over on the newly updated snapshot to its parent. This continues until every snapshot has been committed.

This method can be relatively slow since data farthest from the base disk might be copied several times. More importantly, this method can aggressively use disk space if the snapshots are large, which is especially problematic if a limited amount of space is available on the datastore. The space issue is troublesome in that you might choose to delete snapshots explicitly to free up storage.

This issue is resolved in this release in that the order of snapshot consolidation has been modified to start with the snapshot closest to the base disk instead of farthest. The end result is that copying data repeatedly is avoided.

Just to give an example, 4 snapshots:

Old situation (pre vSphere 4 Update 2)

  • Base disk – 15GB
  • Snapshot 1 – 1GB –> possibly grows to 13GB
  • Snapshot 2 – 1GB –> possibly grows to 12GB
  • Snapshot 3 – 1GB –> possibly grows to 11GB
  • Snapshot 4 – 10GB

Snapshot 4 is copied in to Snapshot 3, Snapshot 3 in to Snapshot 2, Snapshot 2 in to Snapshot 1 and Snapshot 1 in to your Base disk. After the copy of Snapshot 1 in to the Base disk all Snapshots will be deleted. Please note that the total amount of diskspace consumed before the “Delete All” was 28GB. Right before the final merge the consumed diskspace is 61GB. This is just an example, just imagine what could happen with a 100GB data disk!

New situation

  • Base disk – 15GB
  • Snapshot 1 – 1GB
  • Snapshot 2 – 1GB
  • Snapshot 3 – 1GB
  • Snapshot 4 – 10GB

Snapshot 1 is copied in to Base disk, Snapshot 2 is copied in to Base disk, Snapshot 3 in to Base disk and Snapshot 4 in to your Base disk. After the copy of Snapshot 4 in to the Base disk all Snapshots will be deleted. Please note that the total amount of diskspace consumed before the “Delete All” was 28GB. Right before the final merge the consumed diskspace is still 28GB. Not only did VMware reduced the chances of running out of disk space, the time to commit the snapshot by using “delete all” has also been decreased using this new mechanism.

Feedback on VMware Snapshots

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Henry Robinsson, a product manager at VMware, just posted a topic on the VMTN community forums requestion feedback on VMware snapshots. (Thanks William Lam for pointing this out) I am uncertain what this feedback will lead into but usually it is used as guidance for the direction a specific product or feature is heading into.

If you want to be part of the people who directed a VMware feature into a specific direction I would suggest heading over to the survey linked below and fill it out!

I would appreciate it if you could take a few minutes to respond to this survey. Your response will guide our future product offerings in this area. The survey is about 20 questions and should take you just a few minutes to fill out.

I will post a summary of the results after suitable feedback.

Regards,

Henry Robinson
VMware Product Management
The URL to this survey is: http://www.surveymethods.com/EndUser.aspx?B094F8E2B1F2E0E6B6

vSphere VM Snapshots and block size

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As some already noticed; when creating a snapshot on a VM with two disks the block size of the VMFS volume which hold the working directory is checked before the snapshot is taken. As reported by VMTN User Pizang this was not the case in ESX 3.x. You can imagine that this can cause issues when the second disk of a VM is larger than the maximum file size dictated by the block size of the VMFS file system which holds the working directory of the VM. What? Yeah I had to read that sentence at least 3 times before I understood what I said… This might make it easier:

virtualmachine001
Disk01 – 10GB stored on VMFS001 with a 1MB Block size
Disk02 – 350GB stored on VMFS002 with a 4MB Block size

VMFS001 contains the working directory of the vm “virtualmachine001”. Snapshots are stored in the working directory. In the case of Disk02 this could mean that the delta file grows beyond the maximum file limit of 256GB of VMFS001 where it will be stored.

Another example of where the block size could limit you is outlined in this KB article: http://kb.vmware.com/kb/1012384.

Consolidating snapshots

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I was just reading this excellent KB article on consolidating snapshots. It really contains a wealth of information and a procedure on how to remove a snapshot of a disk that has been changed in size for instance.

if the disk has been changed in size the following error will show up during the boot process of the VM:

The parent virtual disk has been modified since the child was created

Read the full article for the solution.