Sony DDS-4, Руководство по описанию продукции

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SONY SDT-10000/SDT-11000 DDS Tape Drive
4. OPERATION
4. 4 TAPE FORMAT
The SDT-10000/SDT-11000 is an implementation of the Digital Data Storage (DDS) format, a standard developed by
Sony and Hewlett-Packard for 4mm data storage drives. It incorporates the error correction techniques used in DAT
audio drives with additional techniques specifically designed to provide the optimum level of data integrity. These extra
methods of error detection and correction are:
- C3 ECC, third level Error Correction Code, providing correction across frames within groups
- Read-After-Write, where data is verified immediately after it is written and re-written if there is any error.
- N-Group Writing, where every group is repeated a set number of times. (DDS, DDS-DC, DDS-2 only)
- Randomizer, to reduce inter-symbol interference.
- Track checksums, to detect and locate helical errors, thereby improving the performance of C3 ECC.
4. 4. 1 Tape Partitions
Tapes can be formatted as a single data space or as two partitions. With two partitions, each has the same structure and
can be written independently. So, for example, the partition further from BOM (Partition 0) can contain data files, and
the partition closer to BOM (Partition 1) could contain a directory of these files, written later.
With the exception of the Device area on the tape, each partition of a 2-partition tape is identical to a single data space
tape in structure. This means each partition has its own Tape Log area; this is necessary because the patterns of usage
may be very different for each partition. Similarly, each has its own Vendor Group, because the partitions might be
written by different drives.
4. 4. 1. 1 Formatting Partitions
The SCSI MODE SELECT command is used to create partitions on a tape. The command can perform the following
operations:
- Set up two partitions on a blank tape.
- Convert a single data space tape to a 2-partition tape.
- Convert a 2-partition tape to a single data space tape.
- Change the size of both partitions on a 2-partition tape.
- Resize the partitions of a 2-partition.
Note: Formatting is not needed for single partition operation.
The MODE SELECT, Medium Partitions Parameters Page (11h) is used to Format the tape.
MODE SELECT, Device Configuration Page (10h) is used to change from one partition to another, see the MODE
SELECT Command description in the SCSI command section of this manual. The LOCATE Command also has the
capability to select a partition prior to positioning.
Any data on the tape before the format pass becomes inaccessible, even if the format pass is intended only to change the
size of the two partitions. The Tape Logs are also destroyed and new logs created.
If you do not format a new tape, it will be organized as a single data space tape. After data has been written to it, whether
it was first initialized or not, a format pass is necessary to alter its characteristics and hence how it is handled by the tape
drive system.
Note: The format operation can be very time consuming depending on the requested size of the first partition on the
tape. The amount of time required can be approximated by use of the following formula:
- Number of Megabytes in Partition 1 x 1.4 = number of seconds required (DDS, DDS-DC, DDS-2)
- Number of Megabytes in Partition 1 x 0.5 = number of seconds required (DDS-3, 4)
- Add about 60 additional seconds for processing overhead