HP C2233 Product Description Manual page 48

Track and Sector
Sparing
3·8 Product Features
distribution is assumed, the calculated probabilities of error
misdetection and miscorrection are as follows:
• Probability of misdetection (an error exists; but ECC does
not recognize it) is less than 1 x 10-
79 •
• Probability of miscorrection (an error is detected, but is
improperly corrected) with CRC is less than
lxlO- 47 •
The HP C2233/34/35 Series disk drives support sector
sparing and track sparing.
Sector sparing is accomplished by "slip formatting" the
track in question. There is one "extra" physical sector
available at the end of each track. If a sector goes bad, the
recoverable data from that sector, and the data from the
following sectors is relocated "downtrack" by one physical
sector. The bad sector is no longer used, and the logical
addresses of the following sectors are re-sequenced to
match the original logical addresses.
Track sparing is implemented for tracks with more than
one defective sector, or when logical block length is not
equal to the physical sector length. Cross-head track
sparing is supported out of a single spare track pool. This
allows for one or more surfaces to have a higher than
normal number of spare operations without loss of drive
operation.
There are nine tracks reserved as spares on each disk
surface, and one sector reserved as a spare in each data
track. Defective tracks that require sparing may all reside
on one surface, at the beginning, middle, or end of a
cylinder, or at random locations. Defects causing a sector
to be spared may
exist
in the header, the data field, or any
other area within the physical sector.
The allocation of spared tracks and sectors is contained
in a "spares allocation" RAM lookup table included in
the microprocessor firmware. The spares allocation table
contains locations for a total combination of 2044 track
DRAFT
10/24/90 11:07
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