You may had experienced the snapshot problem when the snapshot delta virtual disk had become huge which is more than 20GB and is not able to be truncated by removing all the snapshot. Usually the problem occur when the snapshot is no longer available from snapshot manager, but you can see the delta files available from the command prompt or physical folder that contain the Virtual machine images. I experienced the 2nd time now which I am not able to remove the snapshot on a particular virtual machine from snapshot manager and command prompt. The production virtual machine was powered off due to disk full on the specify datastore. This virtual machine contain a previous snapshot which taken 2 weeks before and yet to be truncated. The delta disk had grown up to >20 GB and fully fill up the available space within the data store.

In order to recover the virtual machine, I had to remove all the snapshots on the virtual machine, but the process hang up after 3 to 4 times I tried. You may able to perform this with command and if you are lucky enough, you should able to remove the snapshot by using command. Alternatively, you can also clone a new virtual disk image contain the delta file changes to a whole new virtual disk by using vmkfstools command. This will require quite some times for you to recover the situation mostly the business will not able to wait and it is no guarantee that the recovery will fully work as we expected.

For my case, the quickest way to recover this is to clone the entire virtual machine to a new datastore that have the disk space you require and power it up immediate after the clone. We double checked the entire virtual machines mount point and services, everything require and last file transaction is available without any issue and back to production. Now I will have my sweet time to slowly investigate the failure to remove snapshots on the virtual machines. Well, is not necessary the method I am using here is the best, but I would like to share my personal experience in the critical production time, you may wanna consider the best option to recover the production virtual machine as soon as possible.

I had a tough time this week to deal with the snapshot issue with one of the VM. The VM is containing an important snapshot that previously taken for system restoration. When I browsed through the snapshot manager from vCenter, the system show my VM was running without any snapshots. Here was the kicked start of my problem and excited journey until I managed to recover it this morning.

I tried to SSH to the ESX host and browse to the specified datastore, and I found the snapshot file which end with file extension .vmsn were available in the correct location. No matter how many times I tried and rebooted my Virtual center, the snapshot were not visible to the snapshot manager still.

I read through some articles and forums which suggested to clone the snapshot by using vmkfstools -i option, but it didn’t success in my case here, and I continue my research and here I found a useful blog post from 1 of the blogger  Oliver O’Boyle who experienced similar issue previously.

After I read through his article, which explained the chain within the CID and parent CID, it does help me to resolve my issues. I found that the root cause of my VM was due to the snapshot problem & vmdk config file corruption. For snapshot issues, we can recreate a new snapshots and we select to delete all snapshot afterward, it should force the vmdk flat files and delta files to be committed. In 1 of the virtual hard disk, we experience difficulty as the ESX servers will force the virtual HDD to be detached from the VM. The root cause of that was caused by the file missing on the parent file which should be VMxxxx.vmdk.

During this troubleshooting, you should ensure that the delta files and flat files are always retained and not overwritten. There are 2 delta files which end with VMxxxxx-000001.vmdk and VMxxxxx-000001-delta.vmdk. Your flat file should end with VMxxxxx-flat.vmdk. The 1st thing I did, was to ensure the virtual disk was able to re-attached the vm. I had manually created a new vmdk config file follow the guide from the Oliver O’Boyle, and I copy the parent CID and virtual disk value number require.  I had manually configured the link within .vmdk and the flat file. After that, I was able to attach the virtual disk back to the VM from virtual center. Please take note that the virtual center will not see the flat files as the attachable virtual disk, as vCenter recognize the virtual disk base on the location of .vmdk. Recommended to keep the .vmdk and flat file within same datastore. You can also relocate the vmdk files to different datastore if you wish to do so.

Once the virtual disk had been attached to the VM, boot up the VM immediately. Please log in to the system and ensure everything is in normal and functioning correctly. The data I contained now, wasn’t the latest data I needed as the result of the missing snapshot which was not committed by the system. Now, I take a new snapshot for my entire VM. Once I had done that,  datastore in SSH showed up with plenty of delta files and newly created VMDK files which end with VMxxxxxxx-000003.vmdk and so on.

Here are the steps been taken to commit the snapshots manually

1. Power off the VM
2. Right click the VM and select edit settings from vCenter and select the virtual disk that you are trying to recover. The system will show which vmdk files this virtual disk is pointing to
3. Copy down the file names and go back to your SSH screen
4. Replace the VMDK and delta files that you previous retain from your original snapshots which you are recovering with the FILE NAMES that you copy on step 2
5. Open up the snapshot manager for the VM, and select delete all snapshots option. This process will take time as it depend the size of your delta files require to be committed.
6. It should stuck at 95 % or time out, but the system will still continue to commit the delta files back to the flat files. In my case, it took more than 2 hours to delete the snapshot
7. I noticed the ESX server load and disks activity increased from the performance chart
8. Once it completed, all the delta files will be deleted and everything should be back to normal
9. Power on the VM and double check all the data and mount point and I found the system was back to normal

Have a look here:
VMware ESX VMFS LUNs Report.

I would suggest you try snackcheck and smtp_send.pl scripts provided by YellowBricks.

Sending snapcheck html email from the service console
# /usr/local/bin/smtp_send.pl -t toyouremail@malaysiavm.com -s ” `hostname` Diskspace report of the VMFS volumes” -f fromemailadd@malaysiavm.com -m “`cat /var/log/vdf.html`” -r SMTPserver

Below is step by step guide with screen captured from the VM (my test machine is running on Windows 2003 Enterprise):

Tip: It is best to do a snapshot before you start this task, incase anything goes wrong.

1) This is my test VM machine. It is having one disk at beginning.

2) I am going to add the second disk with 2GB space.

3) Click on Action, then choose "Rescan Disks".

4) Windows detected a new disk.

5) You need to initialize the disk before you can use it.

6) Format it and map it as E:"

Ok, our job done. Now you have a new volume on the Windows box.

Below is step by step guide with screen captured from the VM (my test machine is running on SLES10 SP2):

Tip: It is best to do a snapshot before you start this task, incase anything goes wrong.

1) This is my test VM machine. It is having one disk at beginning.

2) I am adding a 2GB volume into the VM. Click OK to continue.

3) Rescan to detect the new volume just added in VM Properties Screen.

Tip: Run following as root.

In this screen I actually run following commands:

a)# cat /proc/partitions

This will show the current volume in the server, which is the first portion in the screen capture. What we have on the server is only /dev/sda.

b)# rescan-scsi-bus.sh

This command will do a scan for all the /dev/sdx you have on the server. The new volume that we just add will get detected and show as /dev/sdb in my case.

c)# cat /proc/partitions

This is just to show the volume on the server again to confirm I got the new volume detected.

4) run fdisk to create the new Linux volume.

5.1) Format the volume into EXT3 File System.

Or you are using reiserfs? Please refer to following screen capture:

5.2) Format the volume into ReiserFS.

6) modify /etc/fstab to make sure the server will boot up with the new volume.

Modify /etc/fstab by adding a line which point /dev/sdb1 (the new volume) to moint into /sles (your mount point). The screen capture is for ReiserFS. If you are using EXT3, you may replace the “reiserfs” to “ext3” in the same line.

And, your job is done. No reboot required. Have fun.

Due to certain requirement, you may need to clone a snapshot taken sometimes ago and you can make as many copies as you need.

This guide show how to making a clone from a snaphot on VMware Workstation 6.5.

Note: The snapshot MUST BE from a virtual machine that is powered off.

Open VMware Workstation 6.5, click on VM tab, click Snapshot, click Snapshot Manager or CTRL+m.

Click clone.

Click Next on Clone Virtual Machine Wizard.

Click Next Clone from The current state in the virtual machine.

Click Create a full clone and Next.

There are 2 types of clone:
# A full clone is an independent copy of a virtual machine that shares nothing with the parent virtual machine after the cloning operation. Ongoing operation of a full clone is entirely separate from the parent virtual machine.
# A linked clone is a copy of a virtual machine that shares virtual disks with the parent virtual machine in an ongoing manner. This conserves disk space, and allows multiple virtual machines to use the same software installation.

Enter Virtual machine name, Location and click Finish. You’re done!

I’m sure you will ask making a clone from a snapshot for VMware ESX Server. Just do a live clone and revert to snapshot taken or you may refer to VMware Communities Forum.

Enjoy!