Lengthy time for archive creation

[Hanxue Lee <hanxue.developer@gmail.com>]

Tarsnap took >6 minutes to create an archive that contains 108MB of new data. 

$ time tarsnap  --humanize-numbers -c -f mac-virtualbox-20131030  ~/VirtualBox\ VMs/

tarsnap: Removing leading '/' from member names

                                       Total size  Compressed size
All archives                               131 GB            56 GB
  (unique data)                             17 GB           6.9 GB
This archive                                19 GB           8.2 GB
New data                                   297 MB           108 MB

real 6m0.835s
user 3m25.115s
sys 0m4.538s

I thought that is a bit length on a machine with SSD, 16GB RAM and Intel(R) Core(TM) i7-3615QM CPU @ 2.30GHz. 

Is the duration normal?

Will I expect a lengthier duration for archive creation if there are small daily changes and daily tarsnap archive?

Best regards,

Hanxue