1Features
Determining the Tape Format
When writing data to tape, the tape drive does one of the following:
If the tape is positioned at the logical beginning of tape (LBOT), the tape drive writes data in the default format or whatever format you select with the SCSI MODE SELECT (15h) command. (The tape drive allows only one format on any one tape.)
If the tape is positioned at any other valid position for writing data, the tape drive writes data in the same format as the data already on the tape.
When reading a data cartridge, the tape drive automatically determines the tape’s format.
Data Compression
When the tape drive compresses data, it uses the established Improved Data Recording Capability (IDRC) algorithm. Licensed from IBM, this algorithm is the de facto standard in mainframe environments. The tape drives also use the Exabyte Compression Integrity Check™ feature to ensure that data is accurately compressed and decompressed into the original form sent by the initiator.
The compression algorithm is completely contained in an Exabyte proprietary integrated circuit. The tape drive invokes the compression algorithm intelligently, constantly monitoring the compression ratio to determine whether compressing the data will actually decrease the size of the data set. The tape drive sends compressed data to tape only when it benefits the user’s storage capacity and throughput.
Although the actual data compression ratio depends on the type of data, the
For detailed information about how the tape drives compress data, see Chapter 3.
510504 | ||
| (Standard and XL) |
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