than for a drive with rotating heads. DLTtape media is more durable
than other types of media by a very wide margin.
Data Integrity – Error Correction
The important figure in terms of data integrity is the uncorrected bit
error rate, sometimes referred to as the hard error rate. Uncorrected bit
error rate is the number of erroneous bits that cannot be corrected by
error correction algorithms. For DLTtape and Super DLTtape drives,
we have calculated an uncorrected bit error rate of one bit in 10
17
bits.
That is one error in 100 quadrillion bits, or one error in 12 quadrillion
bytes. How does that compare to other technologies? Most DAT drives,
for one example, quote a spec of one uncorrected error in 10
15
bits. 10
15
is 100 times less than 10
17
. Therefore, you can expect 100 times more
errors on the DAT drive than on the DLTtape drive.
Modern high-density tape technologies, which record more data
on smaller segments of tape, have made error correction quite
complex. High-density tape drives have to recover a higher per-
QUANTUM DLTtape HANDBOOK
6.7
1
5
9
13
14
10
6
2
3
4
8
Channel 1
Channel 2
Channel 3
Channel 4
12
16
7
11
15
ECC1
ECC2
ECC3
ECC4
Direction of Tape Motion
PRE
POST
CONTROL
USER
DATA
USER
DATA
USER
DATA
S
Y
N
C
C
R
C
C
R
C
E
D
C
C
R
C
I
N
D
E
X
1
I
N
D
E
X
2
I
N
D
E
X
3
Figure 6-3 A DLT 8000 20-block Data Entity
is shown above. Each
entity contains 16 data blocks and 4 blocks of Error Correction Code, ensur-
ing data integrity.
