Dell Lto5 Manual

							LTO-5 Tape Drive User’s Guide37
Chapter 4
Theory
This chapter describes operational theories used in the LTO-5 Tape Drive.
The topics covered in this chapter are:
•Track Layout
•Recording Method on page 38
•Data Buffer
 on page 39
•Data Integrity
 on page 39
•Data Compression
 on page 41
Tr a c k  L a y o u t
With the LTO-5 Tape Drive, there are 1280 data tracks on the LTO tape, 
numbered 0 through 1279. 
The area between adjacent servo bands is a data band. There are 4 data 
bands, each of which includes 300 data tracks. The data bands are 
numbered 3, 1, 0, 2. 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 20 
data tracks in a data band are data sub-bands. There are 20 data sub-bands 
per data band. The data tracks are accessed in a serpentine manner. 
						

							Chapter 4  Theory
Recording Method
38LTO-5 Tape Drive User’s Guide
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 tape contains 80 track groups, 40 written in 
the forward direction and 40 written in the reverse direction. 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 13
 shows the layout of data on an LTO tape. 
Figure 13  Layout of the Tracks 
on LTO Ultrium Tapes 
Recording Method
The LTO-5 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:
Tape edge
Even # wrap Servo band
Odd # wrap
Tape edge Even # wrap
Servo band Odd # wrapSub-band 0
Sub-band 15 Sub-bands 1 through 14 
(not shown)
Beginning of tape (BOT)End of tape (EOT)Data Band 
						

							Chapter 4  Theory
Data Buffer
LTO-5 Tape Drive User’s Guide39
•ONE is represented by a flux transition at the center of a bit-cell.
•
ZERO is represented by no flux transition in the bit-cell.
Data Buffer
In its default configuration, the LTO-5 Tape Drive has a 256-Mbyte 
buffer. The buffer controller has a burst transfer rate of 320 Mbytes/sec., 
and utilizes bank switching to achieve a maximum average bandwidth 
of nearly 240 Mbytes/sec. The high bandwidth is needed to support 
look-aside data compression in the case of compressible data being 
transferred from the SCSI.
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 adaptive Finite Impulse Response (FIR) filters that 
modify the equalization of each read channel dynamically to 
compensate for many of those changes.
The error rate of the LTO-5 Tape Drive is less than 1 hard error in 10
17 
bits. The undetectable error rate is 1 in 10
27 bits read.
Error-correction Code 
(ECC)
The use of Cyclic Redundancy Checking (CRC), two-level orthogonal 
Error Correction Coding (ECC) provides a very low probability of 
encountering a hard error. During the read process, ECC correction is 
performed on the fly without affecting tape streaming.
There are two levels of Error Correction Coding (ECC). These two levels 
are orthogonal — that is, an ECC codeword at one level intersects ECC 
codewords at the other level just once, which means there will be only  
						

							Chapter 4  Theory
Data Integrity
40LTO-5 Tape Drive User’s Guide
one common symbol between them. The two levels are called C1 and 
C2.
C1 ECC
As data is written to memory from the data processing unit, the DMA/
ECC interface generates C1 ECC bytes and writes them to memory.
As data is written to tape, the C1 ECC is checked and an interrupt 
generated if there is an error. The C1 ECC read from memory is the ECC 
that is written to tape.
When data is read from tape and stored into memory, C1 ECC is checked 
and: 
• If the C1 ECC is good, the “Valid” bit for the codeword pair is set. 
• Otherwise, a pointer to the invalid codeword pair is passed to the 
C1 ECC correction engine. 
• If the C1 ECC correction engine can correct the error, then the 
corrected bytes are written to memory, and the Valid bit is set. 
• Otherwise, the Valid bit is left cleared. 
As data is read from memory to the data processor for decompression, 
the C1 ECC is again checked and an interrupt generated if it is not 
correct.
C2 ECC
C2 ECC involves three distinct operations:
1
Encoding: Generating C2 ECC bytes from data bytes (performed by 
ECC coprocessor hardware).
2
Decoding: Generating ECC syndromes from data and ECC bytes, 
testing for all-zeroes (performed by ECC coprocessor hardware).
3
Correction: Generating corrected data from syndromes.
The correction depends on the number and types of errors involved:
• For one known C1 codeword pair in error in a subdata set (C2 
codeword), the operation is performed by the ECC coprocessor 
hardware. 
						

							Chapter 4  Theory
Data Compression
LTO-5 Tape Drive User’s Guide41
• For two or more known C1 codeword pairs in error, the matrix is 
computed by firmware and the correction is performed by 
hardware.
• For one or more unknown C1 codeword pairs, syndromes are 
generated by hardware, error location is computed by firmware, 
the matrix is computed by firmware and the correction is 
performed by hardware.
Servo-tracking FaultsDuring a write operation, if the servo system detects an error that may 
result in adjacent data tracks being overwritten, the write operation is 
aborted. The write operation will not continue until the correct servo 
tracking is re-established.
Data Compression
Typical data streams of text, graphics, software code, or other forms of 
data contain repeated information of some sort, whether it is at the text 
level where you can readily recognize regular repetitions of a single 
word, or at the binary level where the repetitions are in bits or bytes. 
Although most data is unique and random, the binary level data exhibits 
patterns of various sizes that repeat with varying degrees of regularity.
Storage efficiency is increased if the redundancies or repetition in the 
data are removed before the data is recorded to tape. Data compression 
technology significantly reduces or eliminates redundancies in data 
before recording the information to tape. This increases the amount of 
data that can be stored on a finite medium and increases the overall 
storage efficiency of the system.
With data compression, the redundant information in a data stream is 
identified and represented by codewords or symbols that allow the 
same data to be recorded in a fewer number of bits. These codewords 
or symbols point back to the original data string, using fewer characters 
to represent the strings. Because these smaller symbols are substituted 
for the longer strings of data, more data can be stored in the same 
physical space.
Some important benefits result from data compression in tape drives: 
						

							Chapter 4  Theory
Data Compression
42LTO-5 Tape Drive User’s Guide
• The same amount of information can be stored on a smaller length 
of tape.
• More data can be stored on a given length of tape.
• Performance can more closely parallel to that of high-transfer-rate 
computers.
• More information can be transferred in the same time interval.
Data Compression 
Considerations
In an effective data-compression method, several factors are important:
• The amount of compression, which is measured by the compression 
ratio. This ratio compares the amount of uncompressed data to the 
amount of compressed data. It is obtained by dividing the size of 
the uncompressed data by the size of the compressed data.
• The speed with which data is compressed and decompressed 
relative to the host transfer rate.
• The types of data to be compressed.
• The data integrity of the compressed data.
The amount of compression possible in a data stream depends on 
factors such as:
• Data pattern
• Compression algorithm
• Pattern repetition length
• Pattern repetition frequency
•Object size (block of information to be compressed)
• Starting pattern chosen
The transfer rate depends on factors such as:
• Compression ratio
• Drive buffer size
• Host computer input/output (I/O) speed
• Effective disc speeds of the host computer
• Record lengths that the host computer transmits 
						

							Chapter 4  Theory
Data Compression
LTO-5 Tape Drive User’s Guide43
Data compression algorithms can be tailored to provide maximum 
compression for specific types of data. Because varying types of data are 
encountered in normal day-to-day operating circumstances, however, 
an effective data compression method for a tape drive must serve 
various data types. Additionally, the data compression method must 
adapt to different data types, automatically providing optimum 
handling for all types of data.
Intelligent Data 
Compression
The compressed capacity of the tape is maximized through the use of 
intelligent data compression. The intelligent data compression hardware 
determines the compressibility of each record. If the size of the record is 
larger after a compression attempt than the native (uncompressed) size, 
then the record is written in its native form.
The intelligent data compression utilizes two compression schemes:
• Scheme-1 is a LZ1-based compression scheme using a history buffer 
to achieve data compression.
• Scheme-2 is a pass-through compression scheme designed to pass 
uncompressible data through with minimal expansion.
There are three specific requirements for compliance with the LTO 
specification.
• The output data stream must be decompressible following LTO rules 
to create the input sequence of records and file marks perfectly.
• An LTO compressed data stream may not contain any of the eight 
reserved control symbols.
• While control symbols allow switching to Scheme 2, this should 
never be used by operational software because this capability is only 
for diagnostic and testing purposes.
Software data compression should never be used because the built-in 
intelligent data compression of the LTO-5 Tape Drive is much more 
efficient than software data compression.
The LTO-5 Tape Drive uses a derivative of ALDC-2 lossless data 
compression that includes additional control codes for intelligent data 
compression. 
						

							Chapter 4  Theory
Data Compression
44LTO-5 Tape Drive User’s Guide 
						

							LTO-5 Tape Drive User’s Guide45
Chapter 5
Specifications
This chapter provides technical specifications for the LTO-5 Tape Drive.
The topics covered in this chapter are:
•Physical Specifications
•Power Specifications on page 50
•Drive Performance Specifications
 on page 50
•Environmental Requirements
 on page 52
•Injected Noise Specifications
 on page 53
•Reliability Specifications
 on page 53
•LTO Cartridge Specifications
 on page 55
Physical Specifications
Ta b l e  4 lists the physical specifications of the LTO-5 Half-Height Tape Drive, 
which is shown in figure 14
 and figure 15.
Ta b l e  5
 lists the physical specifications of the LTO-5 Full-Height Tape Drive, 
which is shown in figure 16
 and figure 17. 
						

							Chapter 5  Specifications
Physical Specifications
46LTO-5 Tape Drive User’s Guide
Table 4  Physical Specifications 
(Half-Height LTO-5)
Figure 14  LTO-5 Half-Height 
Tape Drive Dimensions (front)
SpecificationInternal Drive
Without Bezel With Bezel
Height 1.63 inches  
(41.65 mm)1.68 inches  
(42.70 mm)
Width 5.76 inches  
(146.05)5.86 inches  
(148.99 mm)
Length 8.43 inches  
(214.24 mm)
(Max. to end of 
connector) 8.64 inches  
(219.47 mm)
(Max. to end of 
connector) 
Weight 3.13 lb.  
(1.42 kg.)3.25 lb.  
(1.47 kg.)