Medium Optical Disk (RW551/RW552) Library
6–34
EK–MOL80–SV. B01
The Slipping Area is a portion of the User Zone used by the slip sparing
algorithm. Defects found during certification are excluded from use. The user
accessible space is slipped by a corresponding number of sectors into the slip
area.
This area is large enough to account for a maximum of 2048 slip spares.
Any unused sectors in the slipping area are unavailable for user data.
NOTE
The Slipping Area applies only to 650-Mbyte
media
.
Slip Sparing Algorithm
The slip sparing algorithm is used to manage the defective sectors listed in the
PDL during address translation between logical and physical blocks. During an
address translation, the logical blocks are "slipped" past any defective sectors,
thus the name slip sparing.
As an example, suppose there are defective sectors at
physical block addresses 20 and 30, and the user wants the physical address of
logical block 40.
Since physical addresses 20 and 30 have defective sectors they
should be slipped past, so logical block address 20 is now physical block address
21, and logical block address 30 is now physical block address 32, taking into
account both physical blocks 20 and 30 being slipped past.
This would result in
physical block address 42 being the translation for logical block address 40.
This is not a truly accurate example for the following reasons:
1. PDL entries are given in track/sector form, not as block addresses.
The final
translated address must also be in track/sector form.
2. There is a 3-track offset added to the physical block address, 51 sectors for
1024 bytes/sector media and 93 sectors for
512 bytes/sector media.
3. This example does not take into account the effects of Spare Groups
preceding this sector.
The User and Spare Groups are determined after slip
sparing for 650-Mbyte media, and before slip sparing for 1.3-GByte media.
For 650-Mbyte media, slip sparing is always the first step of address translation,
followed by User and Spare Grouping, and replacement sparing.
For 1.3-Gbyte and 2.6 Gbyte media, user and Spare Grouping is always the first
step of address translation, followed by Slip sparing, and replacement sparing.
The data structures for slip sparing and User and Spare Grouping (the PDL and
DDS respectively) are created or updated only during a certification/format
process, such as during a SCSI Format Unit Command.
After certification, any
additional defect management updating is done through the replacement sparing
algorithm.
