It’s free and open source!
It offers a free alternative to VMware. The license costs for VMware are quite large if you are running a big cluster. OpenStack on the other hand is free, open sourced solution. Of course there are some costs; hardware, electricity, administration, OS licence if you decide to run it on RHEL.
You don’t have to take every component that comes with OpenStack. For example you can leave Swift out of your environment if you don’t need storage. OpenStack being open source means you can modify it how you want based on how it fits to your purposes. This also means that you don’t have to wait for your vendor to fix something small in the software that would come in the next update, which can cost money when you can do it yourself.
OpenStack’s Swift is quite versatile. It can be installed on a single server, which uses only one hard drive, but it is at best when installed on multiple servers.
Adding and removing storage nodes is fast and easy. Add the node to the storage ring configuration and re-balance it. Swift starts automatically replicating the stored files to the new node. Replication is done with rsync, fast and efficient software.
Recently PayPal replaced their 80 000 VMware servers with OpenStack. Their main reason was speed, as mentioned earlier it can take months for vendor to release a fix for something small. Full article and reasons can be found here. Another PayPal’s reason was scalability. They get sudden spikes of traffic and OpenStack can help and deploy new virtual machines to balance the load