Tandberg Data Streamer SLR140 XE Kit SCSI Internal Grey 6721693400 사용자 설명서
제품 코드
6721693400
SLR140 Features
D:\SLR140 Features for Reliability and
Performance.doc
Performance.doc
Page 6 of 13
Printed: 30.03.04
15:17
Error Correction Code - ECC Level 10 (RS 64, 54)
The Tandberg SLR140 writes 192 tracks of data on the 0.315-inch media. In addition there are 24
prewritten servo tracks which are used to assure data is always written on the exact correct position on
the tape media.
prewritten servo tracks which are used to assure data is always written on the exact correct position on
the tape media.
Data are written on the tape in blocks of 512 bytes. Each data block consists of:
1. Random Seed – 3 bytes
1. Random Seed – 3 bytes
•
Seed for derandomisation of blocks used by the VR
2
technology
2. Control Bytes - 8 bytes
•
Type of block (data, ECC, etc), block number, etc,
3. Data Bytes – 512 bytes
•
Actual data or other information like ECC(Error Correction Code) data
4. CRC (Cyclic Redundancy Check) Bytes – 4 bytes
•
Calculated number based on the actual data, and used for error detection during read-while-
write and read operations.
write and read operations.
SLR140 features an improved ECC named ECC Level 10 or RS 64, 54. Level 10 means there are 10
ECC blocks while RS 64, 54 are more detailed and mean Read_Solomon, and 64 blocks whereof 54 are
data blocks in an ECC system (ECC Set). This ECC system can correct data in up to 10 concurrent
incorrect blocks when reading the data back.
ECC blocks while RS 64, 54 are more detailed and mean Read_Solomon, and 64 blocks whereof 54 are
data blocks in an ECC system (ECC Set). This ECC system can correct data in up to 10 concurrent
incorrect blocks when reading the data back.
Before written on the tape, the data is sectioned into frames consisting of 108 data blocks and 20 ECC
blocks. In a frame there are two ECC sets – even and odd. Data block 0, 2, 4, … 106 belongs to the
even ECC set, while data blocks 1, 3, 5, …. 107 belong to the odd ECC set. So in a frame there are
calculated 10 ECC blocks for the even data blocks and 10 ECC blocks for the odd data blocks – or 20
ECC blocks per frame of total 128 blocks.
blocks. In a frame there are two ECC sets – even and odd. Data block 0, 2, 4, … 106 belongs to the
even ECC set, while data blocks 1, 3, 5, …. 107 belong to the odd ECC set. So in a frame there are
calculated 10 ECC blocks for the even data blocks and 10 ECC blocks for the odd data blocks – or 20
ECC blocks per frame of total 128 blocks.
A SUPER FRAME consists of four frames (labeled A, B, C and D) are divided among the four
simultaneously written tracks on the tape. This will give a longitudinal distance of 8 blocks (6 mm)
between blocks in the same ECC set or interleave. The idea is to spread the blocks of the same ECC
set as fare away from each other as possible. The blocks of a super frame are distributed across the
four tracks as shown in the figure below.
simultaneously written tracks on the tape. This will give a longitudinal distance of 8 blocks (6 mm)
between blocks in the same ECC set or interleave. The idea is to spread the blocks of the same ECC
set as fare away from each other as possible. The blocks of a super frame are distributed across the
four tracks as shown in the figure below.
Track 0
A0 (e)
D1(o)
C2 (e)
B3 (o)
D4 (e)
C5 (o)
B6 (e)
A7 (o)
A8 (e)
D9(o)
C10 (e)
...
A127(o)
Track 1
B0 (e)
A1 (o)
D2 (e)
C3 (o)
A4 (e)
D5 (o)
C6 (e)
B7 (o)
B8 (e)
A9 (o)
D10 (e)
...
B127(o)
Track 2
C0 (e)
B1 (o)
A2 (e)
D3 (o)
B4 (e)
A5 (o)
D6 (e)
C7 (o)
C8 (e)
B9 (o)
A10 (e)
...
C127(o)
Track 3
D0 (e)
C1 (o)
B2 (e)
A3 (o)
C4 (e)
B5 (o)
A6 (e)
D7 (o)
D8 (e)
C9 (o)
B10 (e)
...
D127(o)
Channel Block Distribution. (e) - Even ECC set, (o) Odd ECC set.
The ECC data is used to recreate data lost during a read operation. Up to 20 completely missing blocks
in a frame can be recreated. Since the blocks are spread over the media with a distance of eight blocks,
there needs to be up to 56 mm or 2.2 inches of missing data on a track on the tape media. This is very
unlikely to happen, and this will only happen if the media is heavily worn or damaged. Media with
such defects as this will be ejected during the write operation as all incorrect blocks are rewritten. More
“normal” errors on the media are small dots of missing magnetic material spread all over the media,
scratches along the media, derbies or dust on the head.
in a frame can be recreated. Since the blocks are spread over the media with a distance of eight blocks,
there needs to be up to 56 mm or 2.2 inches of missing data on a track on the tape media. This is very
unlikely to happen, and this will only happen if the media is heavily worn or damaged. Media with
such defects as this will be ejected during the write operation as all incorrect blocks are rewritten. More
“normal” errors on the media are small dots of missing magnetic material spread all over the media,
scratches along the media, derbies or dust on the head.
For a SUPER FRAME, up to 80 blocks can be recreated given there are not more that 10 concurrent
missing blocks in the same ECC set on the same track. This gives the Tandberg SLR140 an ability to
recreate almost 20% of all data on the whole media.
missing blocks in the same ECC set on the same track. This gives the Tandberg SLR140 an ability to
recreate almost 20% of all data on the whole media.