A restore of a single user or application can easily require loading and reading 10 to 30 cartridges or more. Finding the right cartridges and having each one of them work without failure is a concern. The amount of people required to manage a tape library typically exceeds the number necessary to manage disk as a protection library.
A tape library is typically a serialized resource. Backup jobs are scheduled by priority; resources are switched and allocated to a job. When that job completes, resources are switched again and the process continues; one backup job serialized behind another—all requiring vigilant monitoring and administration.
Disk Workflow Management Simplicity
Disk used for a protection library lets you simultaneously share resources among multiple servers—whether it’s on a Storage Area Network (SAN) or through the network by way of Internet Small Computer System Interface (iSCSI). There’s no monitoring, switching, or hassles. Backup jobs run simultaneously, avoiding the requirement of tape to wait to start a backup job until after the previous one is completed and resources are switched. With disk, multiple streams can run simultaneously. Using iSCSI-enabled disk, you also can easily collect or move data offsite on a WAN for geographically protected data.
Using disk as a protection library, backups are routed through a centralized backup infrastructure; you can even use de-duplication to greatly reduce the total amount of storage required. Overall, you can expect up to a 20 times savings in stored data with significant improvements in backup and restore performance. Using a post-processing approach, there’s no need to continually add servers to keep up with de-duplication load for backups.
Using disk as a Virtual Tape Library (VTL) provides all the advantages of disk as a protection library while letting you write to tape on the back-end if you need data portability, the most useful function of tape for the small to medium enterprise.
Known chemical processes degrade magnetic tape. The binder systems used in today;’s tape are based on polyester polyurethanes. These polymers degrade in a process known as hydrolysis, where the polyester linkage breaks in reaction with water. One of the byproducts of this degradation is organic acid; organic acids accelerate the rate of hydrolytic decomposition by attacking and degrading magnetic particles. A degraded magnetic particle means you can’t read data, which is reported as a permanent read error.
The lifetime of a tape is defined as the length of time a tape can be archived until it will fail to perform and can’t be read, at which point you can expect significant data loss. The degree of hydrolysis of a tape binder system is a critical property that will determine the life of a magnetic tape.
Temperature and humidity dramatically affect shelf life. A 10-degree temperature change can reduce the life of a tape by 10 or more years. If an administrator loads a cart of tapes and takes them to a non-raised-floor room, temperature and humidity changes will accelerate the effects of thermal decay, which will destroy data in as little as five years. Five years is a long time, but no longer than the length of time you normally keep your disk before you refresh it. So, why risk not getting your data back when you know you can with disk?