Today the question came up on one of Jason Boche’s posts about expanding the vCloud Transfer space operations and when that transfer space is used. I dug through some old emails and located a transcript from a conversation I had asking the same question. I got the reply below from someone in engineering.
The Short answer: If there’s a large chunk of data to be copied (any virtual machine or media upload or copy), it will go through the transfer space first. The only exceptions are those that can be explicitly checked for and optimized away internally (source and destination is the same datastore, in the same cluster of the same vCenter, stuff like that). So some examples are:
- Catalog to mycloud/ catalog to catalog / vApp to vApp / vApp to catalog (SAME Org vDC): NOT transfer store
- catalog to mycloud/ catalog to catalog/ vApp to vApp/ vApp to catalog (DIFFERENT Org vDC): possibly/probably transfer store (depends on Org vDCs and their vCenter+cluster+datastore consanguinity)
- Ovf/iso uploads: transfer store
- Import from vCenter (to orgvdc on SAME cluster or vCenter): NOT transfer store
- Import from vCenter (to Org vDC on DIFFERENT cluster or vCenter): transfer store
The IOPS associated are whatever the network plus the datastore can handle; the usage pattern is almost exclusively bulk sequential writes/reads, as if for a file server that gets a very small number of requests for very, very large files.