A software-based D2D2T solution
Original Publication Date: 2005-Mar-24
Included in the Prior Art Database: 2005-Mar-24
The backup of data to disk is a popular method for data protection. A typical approach is to backup data to a disk first and then to migrate or copy the data from the disk to tape in a second step (disk to disk to tape, D2D2T). In many situations this approach reduces the time needed for backup and restore operations and it improves the utilization of tape drives. While this type of hierarchical storage management is an in-built feature of sophisticated backup applications (e.g. IBM Tivoli Storage Manager(1)), more and more Virtual Tape Systems (VTS) become available on the market. These systems emulate certain models of tape devices and tape cartridges to the server while they store the received data on a disk. This paper describes a third approach for D2D2T backup.
A software A softwareA software A software -
---based Dbased Dbased D based D2
D2222T solutionT solutionT solution
Architecture ArchitectureArchitecture Architecture
Our proposed solution is based on a new device driver which emulates a tape device in the operating system of the server where the backup application writes the data to the backup media (Figure 1). This new device driver presents virtual tape drives and virtual tape cartridges to the backup application whilst it redirects all I/O to files which resides in a file system on disk. The read and write operation on the virtual tapes is simply mapped to read and write operation on files . In a similar way, tape positioning commands like forward and rewind are mapped to seek commands . At the end, applications assume that they are working on a tape cartridge while the I/O is redirected to a file.
Backup A p p lic a tio n
rive Em ulator
file s y s te m
Figure 1. The tape device driver redirects all I/O to a file. The application assumes that it works on a tape cartridge but in real it is working on a local file.
Having this new device driver in place it is straight forward to implement a distributed Virtual Tape Library (Figure 2). The Virtual Tape Library provides a media changer interface (library manager) which can be used by the application to mount and unmount cartridges. This means the new device driver translates library related commands to operations in the file system. E.g. when an application mounts a tape cartridge the new device driver opens the appropriate file. After that the backup application operates on the virtual cartridges as described above. If the files are located in a SAN-based file system then later on the files (=virtual cartridges) can be destaged to physical tape cartridges without using resources on the application server (application server-free backup). The required data mover can be implemented very easily because it just copies files (= virtual cartridges) from the file system to the back-end storage such as physical tapes (repository for virtual cartridges).
Tape Drive Emulator
Library Manager of Virtual Tape Library