Shadowcopy to utilising all space?

Hi Everyone,

I currently have VSS configured on a 2008 R2 server. It will only list 1 weeks worth of snapshots for any given directory. My understanding is that VSS will use as much space as it can to provide as much retention as possible. If I run vss admin I get the following result:

Shadow Copy Storage association

   For volume: (E:)\\?\Volume{748a335c-9ce9-4505-b68e-1ce06fd2e3a5}\
   Shadow Copy Storage volume: (E:)\\?\Volume{748a335c-9ce9-4505-b68e-1ce06fd2e3a5}\
   Used Shadow Copy Storage space: 285.172 GB (8%)
  Allocated Shadow Copy Storage space: 285.596 GB (8%)
 Maximum Shadow Copy Storage space: 558.736 GB (15%)

From reading this, it appears VSS can have more retention. Therefore, why are my snapshots limited to 1 week retention?

Thanks,

David