Recently a couple of consultants brought some unexpected behavior of vCloud Director to my attention. If the provider vDC is connected to a datastore cluster and a virtual disk or vApp is placed in the datastore, vCD displays an error when the datastores do not have enough free space available.
Last year I wrote an article (Storage DRS initial placement and datastore cluster defragmentation) describing storage DRS initial placement engine and it’s ability to move virtual machines around the datastore cluster if individual datastores did not have enough free space to store the virtual disk.
I couldn’t figure it out why Storage DRS did not defragment the datastores in order to place the vApp, thus I asked the engineers about this behavior. It turns out that this behavior is by design. When creating vCloud director the engineers optimized the initial placement engine of vCD for speed. When deploying a virtual machine, defragmenting a datastore cluster can take some time. To avoid waiting, vCD reports an error of not enough free space and relies on the vCloud administrator to manage and correct the storage layer. In other words, Storage DRS initial placement datastore cluster defragmentation is disabled in vCloud Director.
I can understand the choice the vCD engineers made, but I also believe in the benefit of having datastore cluster defragmentation. I’m interested in your opinion? Would you trade initial placement speed over reduced storage management?