VHD Size Backup?

Question

I have a question for DPM server. If there is a dynamic disk 600 GB or Fixed 600 gb, and It has got 300 gb data on it.
how does dpm backs it up? Does it back up full size of the VHD or only the data 300 Gb. on our DPM I can see something strange and it backs up the full VHD size, but wanted to re-check on it.
Thanks,

Answer 1

HI,
Lets take these separately, because behavior will be different.
1) Dynamically expanding VHD
a. When you created the .vhd it was logically 600GB, but physically only was only 1MB in size as no data has been written to it yet.
b. You use DPM to protect the VM containing the .vhd and DPM brings over the 1MB .vhd file.
c. In one day 300GB is written to the .VHD, the logical size is still 600GB, but the physical size has now grown to 300GB.
d. DPM backup will now be protecting a 300GB .vhd file and will bring over those changes and apply them to the .vhd on the DPM replica.
e. As time goes on you eventually get close to filling the .VHD with more data and the .VHD grows to 599GB.
f. DPM again will be protecting the whole .VHD and will bring over those new blocks (299gb) and apply them to the .vhd on the replica, new size is is now 599GB.
g. If you now delete 300GB of data on the .VHD, there will only be 299gb worth af actual files, but the .VHD never shrinks.  DPM will delete the same 300GB worth of files on the REPLICA but .vhd is still 599GB.
h. If you want to shrink the .vhd, you need to run a disk defrag inside the VM, then a compact in Hyper-v. Once the .vhd is compacted, it's new physical size will be smaller - lets say 400GB
g. DPM will see that the .vhd is now smaller and will apply the same changes on the DPM replica., so now the .VHD is 400GB
Fixed Size VHD.
a. When you created the .vhd it was logically 600GB, and physically 600GB in size.
b. You use DPM to protect the VM containing the .vhd and DPM brings over the entire 600GB .vhd file.
c. In one day 300GB is written to the .VHD, the logical size and physical size is still 600GB.
d. DPM backup will bring over those changes and apply them to the DPM replica which is also 600GB in fixed size.
e. As time goes on you eventually get close to filling the .VHD with more data.
f. DPM again will be protecting the whole .VHD and will bring over those new blocks (299gb) and apply them to the replica and the .vhd is still 600GB fixed size.
g. If you now delete 300GB of data on the .VHD, there will only be 299gb worth af actual files, but the fixed size.VHD never shrinks.  DPM will delete the same 300GB worth of files on the .VHD in the REPLICA, but .VHD remais at 600GB fixed size..
DPM Tape backups.
DPM will always backup the entire physical size of the .VHD files.  In the case of fixed size .VHD's that will remain a constant (600GB in this case)  for dynamically expanding, the size of the .VHD may vary as data is written or a defrag and compact
is performed.
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