Information Technology Reference
In-Depth Information
Table 9.2:
Snapshot demonstration results
VMDK
Size
NTFS
Size
NTFS Free Space
Start (pre-fi rst snapshot)
win2k12-01.vmdk (C:)
8.6 GB
40 GB
31 GB
First snapshot (pre-data copy)
win2k12-01.vmdk (C:)
8.6 GB
40 GB
31 GB
17.4MB
win2k12-01-000001.vmdk
First snapshot (post-data copy)
win2k12-01.vmdk (C:)
8.6 GB
40 GB
28.1 GB
3.1 GB
win2k12-01-000001.vmdk
Second snapshot (pre-data copy)
win2k12-01.vmdk (C:)
8.6 GB
40 GB
28.1 GB
win2k12-01-000001.vmdk
3.1 GB
win2k12-01-000002.vmdk
17.4 MB
Second snapshot (post-data copy)
win2k12-01.vmdk (C:)
8.6 GB
40 GB
25.2 GB
win2k12-01-000001.vmdk
3.1 GB
win2k12-01-000002.vmdk
3.1 GB
As you can see from Table 9.2, the VM is unaware of the presence of the snapshot and the
extra VMDK i les that are created. ESXi, however, knows to write changes to the VM's virtual
disk to the snapshot VMDK, properly known as a delta disk (or a differencing disk ). These delta
disks start small and over time grow to accommodate the changes stored within them.
Despite the storage efi ciency that snapshots attempt to maintain, over time they can eat
up a considerable amount of disk space. Therefore, use them as needed, but be sure to remove
older snapshots on a regular basis. Also be aware there are performance ramii cations to using
snapshots. Because disk space must be allocated to the delta disks on demand, ESXi hosts must
update the metadata i les (i les with the .sf i lename extension) every time the differencing disk
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