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|Pick the right tape format|
While there's no magic formula for picking exactly the right tape format for your organization, growing capacities, higher throughputs and different media types make some tape formats better suited for your environment than others. Here are some factors to consider:
Tape format tradeoffs
The choice of higher capacity vs. higher speed depends on a number of factors. In shops where tape is the primary target for backups, the flow of data from the server to the tape drive during backup may fluctuate, which can cause a backhitch (a repositioning of the tape by the tape drive). Tape formats like AIT and SAIT are less susceptible to backhitches because they use drives that lay the data down on tape using rotary heads, which makes the tape move slower. If the backup data flow is interrupted, it takes less time to reposition the tape than with linear tape formats, such as LTO or 3592, which rapidly lay down data by streaming the tape media through the tape drive.
Some tape drives that support linear tape formats, like IBM's TS1120 and Sun's StorageTek T10000, are taking steps to minimize the occurrence of backhitches. These two drives have a speed-matching feature that automatically changes the speed of the tape by sensing the incoming speed of the data. The TS1120 includes six options--50MB/sec, 60MB/sec, 70MB/sec, 80MB/sec, 90MB/sec and 100MB/sec--while the T10000 provides two speeds, 50MB/sec and 120MB/sec.
In shops deploying a disk-to-disk-to-tape backup process, the time restrictions to move data to tape are generally less constraining than when backing up data to disk. For users with longer windows to move the data from disk to tape--and who are less concerned about fast restore and access times--larger, slower moving tape formats like DLTtape S4 or SAIT may be the best choice. For instances where it's necessary to quickly move and restore data to and from tape, formats with higher native throughputs, like LTO or the StorageTek T10000, should be considered. Users employing tools like hierarchical storage management and accessing data on tape, may prefer 3592 tape formats that include "mile posts," markers on the tape at four-meter intervals that help pinpoint where the data lies. If data encryption is required, higher capacity tapes may be preferable because encryption eliminates the option of compressing the data.
This was first published in May 2006