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If a low-density data cartridge MIR is invalid, it is not read into the T9840C drive
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memory, and not available for user data pointer information. Therefore, T9840C
performance for a low-density data cartridge with an invalid MIR is degraded.
Since a T9840C tape drive cannot correct nor rebuild a low-density data cartridge
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invalid MIR, the only options for increasing performance are:
i. Migrate the data to a high-density format cartridge, using a copy utility with a
ii. Rebuild the MIR with a T9840A/B tape drive
iii. Operate with degraded performance
On subsequent mounts, the T9840C drive first sees the tape-resident FIB, identifies the
tape cartridge as low-density, and reads the low-density MIR into drive memory. At
dismount, the T9840C updates the tape-resident FIB with cumulative data, including
newer statistical data from the MIR, if the cartridge had been loaded into a T9840A/B
drive since the last mount in a T9840C drive.
T9840A/B Tape Drives
When a high-density data cartridge is loaded into a T9840A/B drive with appropriate
level firmware, the drive looks for a low-density MIR at the default location but finds a
Format Identity Burst (FIB), which identifies the cartridge as formatted in a high-
density. Since the T9840A/B drive cannot read nor write higher-density data,
subsequent normal read/write attempts will fail unless the cartridge is being reclaimed.
A T9840A/B drive cannot update statistical data, such as the mount/dismount count in
the FIB. Therefore, cumulative statistical data will not include mounts into a T9840A/B
drive as long as the tape cartridge is in high-density format.
The tape cartridge could be deliberately over-written in low-density data format from
the beginning-of-tape point, or reformatted to low-density data format by the offline
Drive Operation, Make Data Tape submenu. Either case over-writes the FIB with a low-
density MIR, and erases the high-density MIR. Such a reformatted data cartridge is no
longer identifiable as a high-density data cartridge, but does include the statistical data
read from the FIB.
When a low-density data cartridge with a tape-resident FIB (created by a T9840C or
T9840D drive) is loaded into a T9840A/B drive with appropriate level firmware, the
MIR is read into drive memory and an invalid flag is written to the tape-resident MIR.
During the unload routine, the T9840A/B drive compares statistical data in the tape-
resident MIR with statistical data in the tape-resident FIB, and uses the latest data to
calculate the statistical data update into the new tape-resident MIR.
Notes:
The T9840A/B drive shows Ready H on the operator panel when a cartridge
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written by a T9840C or T9840D drive is loaded.
If the last load was into a T9840A/B drive, the tape-resident MIR will contain the
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latest statistical data; whereas, if the last load was into a T9840C or T9840D drive,
the tape-resident FIB contains the latest data.
In order to recognize a high-density data cartridge written by a T9840C or T9840D
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drive, and to properly handle a low-density data cartridge that has been
previously loaded into a T9840C or T9840D drive, T9840A/B drives must have the
appropriate drive firmware level, see
95739 • Revision YA
second T9840C drive
Mixed Media Management
"Mixed Media Management" on page
Chapter 1 Overview 35
31.
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