QUANTUM DLTtape HANDBOOK
5.7
outrigger islands help wipe contaminants such as dust from the
tape as it passes. Like tiny stationary squeegees, these non-ener-
gized islands continuously clean the DLTtape media, ensuring
proper tape/head contact, and data integrity.
A low-stress tape path, contoured head, and self-cleaning design
team up to provide up to 1,000,000 tape passes. All DLTtape car-
tridges provide a shelf life of up to 30 years with just a five percent
loss in magnetic strength.
Error Detection
One quarter of the data on a DLTtape cartridge is dedicated to error
detection and correction. An application-specific integrated circuit
(ASIC) chip containing a custom Reed-Solomon error-correction
code (ECC) maintains unfailing data security. For every 64Kbytes of
user data, there are 16Kbytes of ECC added. For every 4Kbytes of
user data, a 64-bit cyclic redundancy code (CRC) and a 16-bit error-
detection code (EDC) are also added. In addition, each user record is
tagged with an overlapping 16-bit CRC. To top it off, all DLTtape
drives perform a read after each write command, and will automati-
cally re-record data on a parallel channel.
This Parallel Channel Architecture (PCA) maximizes rewrite effi-
ciency. Even with one or more channels inoperative due to bad
blocks, four-channel DLT 7000 and DLT 8000 drives can continue
to write data on a parallel channel (see Figure 5-6). (The dual-
channel DLT 4000 drive also uses the PCA block structure and can
continue operation even with one channel blocked.)
Thanks to multiple levels of error detection and correction,
DLTtape drives offer an exceptional level of data integrity. It has
been calculated that DLTtape drives have an unrecoverable hard
error rate of one in 10
17
bits and one undetected soft error in 10
30
bits. That is a standard that no other tape drive comes close to.
