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Theory
Dell™ PowerVault™ LTO-4-120 Tape Drive User's Guide
This chapter describes operational theories used in the Dell PowerVault LTO-4-120 Half-Height tape drive.
Track Layout
Recording Method
Data Buffer
Data Integrity
Data Compression
Track Layout
With the PowerVault LTO-4-120 Half-Height tape drive, there are 896 data tracks on the LTO tape, numbered 0 through 895. Data track 895 is the track
closest to the bottom edge of the tape (the reference edge).
The area between adjacent servo bands is a data band. There are 4 data bands, each of which includes 224 data tracks. The data bands are numbered 2, 0,
1, 3. Data band 2 is closest to the bottom edge of the tape.
A track group is a set of tracks that is recorded concurrently. The sets of 14 data tracks in a data band are data sub-bands. There are 16 data sub-bands per
data band. The data tracks are accessed in a serpentine manner.
A wrap is a track group recorded in the physical forward or physical reverse direction. The wraps are recorded in a serpentine fashion starting in data band 0.
The LTO-4 tape contains 56 track groups, 28 written in the forward direction and 28 written in the reverse direction. For each, even-numbered wraps are
recorded in the forward direction (BOT to EOT), and odd-numbered wraps are recorded in the reverse direction (EOT to BOT).
Figure 5-1
shows the layout of data on an LTO tape.
Figure 5-1. Layout of the Tracks on LTO Ultrium Tapes
Recording Method
The PowerVault LTO-4-120 Half-Height tape drive records data using write-equalized (0,13/11) Run Length Limited (RLL) code. RLL (0,13/11) Data bits are
defined as follows:
ONE is represented by a flux transition at the center of a bit-cell.
l
ZERO is represented by no flux transition in the bit-cell.
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Data Buffer
In its default configuration, the PowerVault LTO-4-120 Half-Height tape drive has a 128-MB buffer. The buffer controller has a burst transfer rate of 320
MB/sec, and utilizes bank switching to achieve a maximum average bandwidth of nearly 240 MB/sec. The high bandwidth is needed to support look-aside data
compression in the case of compressible data being transferred from SCSI at 160 MB/sec.
NOTE:
Data buffer size and speed do not directly correlate to drive throughput or speed.
Data Integrity
The mechanical and electrical design of the drive ensures that drive performance does not degrade over time. Changes in head alignment, head wear,
component drift, and other factors are minimized to ensure that data integrity and interchange capability are not compromised. The drive also incorporates
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