delta.vmdk

[RanjnaAggarwal]

I heard this from someone that delta.vmdk size cannot exceed beyond the flat.vmdk size means if used hard disk space of a vm is 1gb and then you took a snapshot a delta.vmdk is created and delta.vmdk cannot grow beyond the 1gb and then new delta.vmdk is created. Is this true? If anyone has any experience in this please share this.

[Dave_Mishchenko]

It is the provisioned size that it won't exceed.  If you configure a VM with a 40 GB drive, the delta won't exceed that size.

If you create a new thin provisioned VM and immediately snapshot it,  the virtual disk snapshot will grow as you consume space while the base disk flat file will remain at 0 bytes in size.

[UmeshAhuja]

Hi,

The –delta.vmdk files are only used when snapshots are created of a virtual machine. When a snapshot is created, all writes to the original –flat.vmdk are halted and it becomes read-only; changes to the virtual disk are then written to these –delta files instead.

The initial size of these files is 16 MB and they are grown as needed in 16 MB increments as changes are made to the VM's virtual hard disk. Because these files are a bitmap of the changes made to a virtual disk, a single –delta.vmdk file cannot exceed the size of the original –flat.vmdk file.

A delta file will be created for each snapshot that you create for a VM and their file names will be incremented numerically (i.e., myvm-000001-delta.vmdk, myvm-000002-delta.vmdk).

These files are automatically deleted when the snapshot is deleted after they are merged back into the original –flat.vmdk file.

[rickardnobel · Accepted solution]

Ranjna Aggarwal wrote:

a vm is 1gb and then you took a snapshot a delta.vmdk is created and delta.vmdk cannot grow beyond the 1gb and then new delta.vmdk is created. Is this true?

No, it is not true that a new delta file will be created, but it is true that the delta file can only be maximum the same file size as the original vmdk file.

A new delta is only created if the administrator creates a new snapshot.

[RanjnaAggarwal]

Hi Rickard,

"but it is true that the delta file can only be maximum the same file size as the original vmdk file."

I want to be sure that in this line are you talking about the allocated disk space to the vm?

[a_p_]

To be precise, the delta file can become slightly larger than the provisioned size of the virtual disk. This is due to the sparse format of the delta disk, i.e. the metadata contained in this file. Table "Calculating the overhead required by snapshot files" in http://kb.vmware.com/kb/1012384 shows the size of the overhead for different provisioned disk sizes.

André

[depping]

Btw, things like these can easily be tested or found in either the KB or Doc set.

[rickardnobel]

Ranjna Aggarwal wrote:

Hi Rickard,

"but it is true that the delta file can only be maximum the same file size as the original vmdk file."

I want to be sure that in this line are you talking about the allocated disk space to the vm?

Yes, plus some small amount of extra space as indicated by a.p.

The general point is that a VM with a VMDK file of 100 GB and a snapshot is created = original file in readonly and all writes are commited to the delta. However, the point is that if a single sector is overwritten multiple times only the latest change is keeped, which is the reason for that the maximum delta size is about the same as the original.