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Data Layout

There are three factors which complicate data layout on a disk. [RW94]

1.
zoning To maximize storage capacity, adjacent disk cylinders are grouped into zones. Zones near the outer edge have more sectors per track than zones near the inner edge. The outer zones have higher data transfer rates. [RW94]
2.
track skewing Sector zero on each track is skewed by just the right amount to handle worst case head or track switching times. Each zone has its own skew factors. [RW94]
3.
sparing Also called slipping or forwarding, this is the process by which references to bad sectors are remapped to other spare locations on the disk. In one technique a bad sector or track is remapped elsewhere. A more complicated technique, called slip sparing or slipping, is to shift all of the sectors after the bad sector by one sector or track. [RW94] [SG94] Sparing complicates disk optimization since the good sector may or may not be near the bad sector. [SG94]



Barnett Hsu
1998-10-31