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You can change the density by pressing the Density switch on the front panel
when the drive is in the standby condition or when it is offline and the tape is at
BOT. The Density switch is disabled when the drive is online.
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The host can change the density when the drive is online and the tape is at
BOT.
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The tape drive itself can change the density when reading or writing from BOT.
This feature is referred to as automatic density selection or ADS for short.
3.6
Automatic Density Selection Feature (ADS)
With some tape drives, you have to know the density of the tape to be read ahead of
time and configure the drive to read that density. If you set one of these drives to a
density other than that on the tape and then attempt to read the tape, read errors
will result. To overcome this, 34XX tape drives incorporate Automatic Density Select
(ADS). ADS determines the drive's operating density when read or write commands
are received while the tape is at BOT. This section describes the operation of ADS.
3.6.1
Density Definitions
To understand ADS, you should first be familiar with certain terms and definitions.
3.6.1.1 Initial Density
The term initial density refers to the value of the INITIAL DEN: parameter in the
Drive Configuration menu. This value is stored in non-volatile memory and is used
to define the write density each time you apply power to the drive.
3.6.1.2 Write Density
The write density appears on the left side of display line one and is the density at
which the drive will write. Each time you apply power to the drive, the write density
assumes the value of the INITIAL DEN parameter.
You can change the write density via the Density switch if:
1.
The tape drive is offline and the tape is at BOT, or
2.
The drive is in the standby state (i.e., the tape is unloaded);
The host can change the write density if the tape drive is online, the tape is at BOT,
and the Density Command option is enabled (see Section 4.3.2.14).
The tape drive can change the write density as explained in Section 3.6.2.
3.6.1.3 Read Density
The term read density refers to the density at which the drive will read the tape. If
the read density is not the same as the density of the tape, read errors will occur.
3-8
Operating Instructions
500300 Rev. U
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