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TechNote:
Virtual Tape Libraries
Virtual Tape Libraries for Disk-to-Disk Backup
Backup and Recovery, despite many technical advances, is the most failure-prone process in the data-center environment. Industry estimates for failure rates of backup jobs range from 10% to 20% or more. Data growth has narrowed the window for backups, and data restoration from tape is a lengthy and costly process better reserved for disaster recovery or deep archival recoveries.
larger imageThe primary benefits of using disk as a backup medium are reliability of backup job completion, and rapid near-term data recovery. Restoration from tape can be slow, may require substantial management by the storage administrator, and involve delays in delivery of tapes from off-site storage.
Using a disk target for backup can be 10 times faster than tape, and eliminates the risks of data loss from tape failures. Once a backup image is secured on a disk, it can be re-directed to tape during regular data-center working hours for longer-term and/or off-site archival purposes. Recovery from an on-site disk will be 5 to 10 times faster.
IT administrators now prefer Virtual tape Libraries (VTL's) because they have discovered that there are a number of unexpected challenges with generic host-based Disk to Disk (D2D) backup strategies that use the limited capabilities of general-purpose disk and file systems.
- Combining VTL software and storage from separate vendors, often leads to integrations issues requiring changes in backup strategies.
- The physical storage to be used for D2D backup still requires separate storage management tasks to work around volume-sizes and other limitations.
- Partition and individual file size limitations arise with general-purpose file systems like FAT, NFS, and NTFS.
- General-purpose RAID arrays and file systems are not optimized for streaming D2D backup.
- Gradual file system fragmentation causes degraded performance.
- Security breaches, virus attacks and data corruption risks are possible with general-purpose file systems used for D2D.
Key Point Summary
Tape vs. Disk:
- Tape and Disk have complimentary roles for backup.
- Tape is preferred for archival.
- Disk is up to 10 times faster for backup and restores.
- Disk accommodates start-stop or data-starved streams better than tape.
Disk-to-Disk Issues:
- Common file systems are not optimized for backup.
- Storage array management costs reduce the ROI for D2D backup.