Compaq ProLiant 1000 DDS-3 Enhancing DAT Reliability, Capacity, and Performanc - Page 8

Improved Reliability

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ECG036/1297 7(&+12/2*< %5,() (cont'd) ... DDS-3's read-after-write (RAW) capability also improves the data transfer rate. RAW refers to the ability of a DDS drive to read and verify data immediately after it has been written. This is possible because of the extra set of read and write heads that DAT drives have. In the event of an error, the drive can rewrite the incorrect data repeatedly until it is read back successfully. This ability eliminates the need for a time-consuming validation phase. Improved Reliability DDS-3 technology offers improved reliability over DDS-1 and DDS-2 technology with better error detection and correction and a more effective automatic head cleaner. (UURU 'HWHFWLRQ DQG &RUUHFWLRQ DDS formats have three levels of error correction code (ECC): C1, C2, and C3. Additional error detection and correction techniques, such as RAW, data randomizing, checksums, and Ngroup writing, are also features of DDS-3. These techniques, combined with ECC, provide an extremely high level of data integrity. DDS-3 has improved C1 error detection over DDS-1 and DDS-2. DDS-3 is able to distinguish which block in a block pair is bad and correct only the bad block. This ability decreases the verall error rate since two C1 errors are assumed for every C1 correction with DDS-2. It also decreases the need for C2 correction, which is used when the maximum number of C1 corrections is reached. Additionally, DDS-3 knows what correction needs to be applied to data before it reached Error Correction Code. This ability allows for spending more time on correction than detection. 'ULYH &OHDQLQJ One of the best ways to avoid errors is to clean the tape heads regularly1. In addition to cleaning the drive regularly with a cleaning tape, DDS-3 has an automatic head cleaner that touches the head every five minutes of tape movement to remove debris during the write or read recovery procedure. Automatic head cleaning also occurs when normal error correction fails. The DDS-3 internal head cleaner has an improved design, which provides more effective cleaning over the latest DDS-2 designs. The new sweeper brush (Figures 7 and 8) cleans the head better than previous foam head cleaners. This eliminates occurrences of head-to-tape separation, reducing error rates. The automatic head cleaner enhances reliability and reduces user maintenance requirements, reducing the frequency of cleaning by a conservative factor of four. Figure 7: DDS-3 head cleaner. Figure 8: DDS-3 head cleaner in DAT drive. 1 For information on cleaning DAT drives, please see white paper, Tape Drives, Media, and the Importance of Cleaning, document number ECG079.1197. 

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(cont’d)
ECG036/1297
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DDS-3’s read-after-write (RAW) capability also improves the data transfer rate.
RAW refers
to the ability of a DDS drive to read and verify data immediately after it has been written.
This
is possible because of the extra set of read and write heads that DAT drives have.
In the event
of an error, the drive can rewrite the incorrect data repeatedly until it is read back successfully.
This ability eliminates the need for a time-consuming validation phase.
Improved Reliability
DDS-3 technology offers improved reliability over DDS-1 and DDS-2 technology with better
error detection and correction and a more effective automatic head cleaner.
DDS formats have three levels of error correction code (ECC): C1, C2, and C3.
Additional
error detection and correction techniques, such as RAW, data randomizing, checksums, and N-
group writing, are also features of DDS-3.
These techniques, combined with ECC, provide an
extremely high level of data integrity.
DDS-3 has improved C1 error detection over DDS-1 and DDS-2.
DDS-3 is able to distinguish
which block in a block pair is bad and correct only the bad block.
This ability decreases the
verall error rate since two C1 errors are assumed for every C1 correction with DDS-2.
It also
decreases the need for C2 correction, which is used when the maximum number of C1
corrections is reached.
Additionally, DDS-3 knows what correction needs to be applied to
data before it reached Error Correction Code.
This ability allows for spending more time on
correction than detection.
One of the best ways to avoid errors is to clean the tape heads regularly
1
.
In addition to
cleaning the drive regularly with a cleaning tape, DDS-3 has an automatic head cleaner that
touches the head every five minutes of tape movement to remove debris during the write or
read recovery procedure.
Automatic head cleaning also occurs when normal error correction
fails.
The DDS-3 internal head cleaner has an improved design, which provides more effective
cleaning over the latest DDS-2 designs.
The new sweeper brush (Figures 7 and 8) cleans the
head better than previous foam head cleaners.
This eliminates occurrences of head-to-tape
separation, reducing error rates.
The automatic head cleaner enhances reliability and reduces
user maintenance requirements, reducing the frequency of cleaning by a conservative factor of
four.
Figure 7: DDS-3 head cleaner.
Figure 8: DDS-3 head cleaner in DAT drive.
1
For information on cleaning DAT drives, please see white paper,
Tape Drives, Media, and the Importance of
Cleaning,
document number ECG079.1197.