New tape formats are bigger, faster & safer


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Pick the right tape format

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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 is the initial target. If you're still using tape as the primary target for disk, consider using helical scan formats like AIT and SAIT that use a rotating head to lay the data down on tape. The tape media moves slower, so uneven rates of backup traffic are less likely to cause backhitches and slow backup jobs.

  • Tape is the secondary target. Linear tape formats will generally lay down data faster than helical scan formats when moving data from disk to tape. However, avoid the DLT family of tapes if your transfer windows from disk to tape are tight. The DLT family is starting to follow a roadmap where the growth of tape capacity isn't proportional to the increase in transfer rates.

  • Mixed mainframe, Unix and Windows environments. For enterprises looking to consolidate to a single tape format, consider the 3592, 9840, 9940 and StorageTek T10000 formats that allow the use of one tape format for multiple, different backup packages. Though upfront costs are higher compared to some of the other formats, using one media across the enterprise should drive significant savings.

  • Backwards compatibility. Most new tape generations aren't backwards compatible with preceding generations.

  • WORM support. Though WORM tapes represent only a small percentage of the total tapes shipped, vendors report growing demand from the government, healthcare and retail sectors. Users should verify that the tape format either supports WORM now or has WORM support on its roadmap. You also need to decide if you want to turn on WORM functionality for any cartridge (as with SDLT formats) or purchase separate WORM media.

  • Tape capacity. Vendors are achieving higher capacities by making tape media longer or packing more data into smaller spaces (or both). But this can lead to longer data access times and wasted tape capacity because older tape drives can't read the newer, high-capacity tape formats. However, some tape formats like 3592 offer several cartridges with different capacities and tape lengths.

  • Encryption. Encrypted data can't be compressed, so only rated native capacities should be used for planning purposes.

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

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