Backing up virtual machine operating system data on sequential-access data storage systems is provided. A virtual machine boots into an operating system using operating system data that is provided to the virtual machine from a random access storage unit. The random access storage unit stores the operating system data as a first plurality of blocks. The operating system data is recorded in a sequential order as it is provided to the virtual machine. The operative system data is recorded in a record file. Sequential boot data is recorded on a sequential backup system based, at least in part, on the record file. The sequential boot data is a copy of the operating system data that represent the operating system as a second plurality of blocks based, at least in part, on the sequential order of the operating system data provided to the virtual machine.