Appeal No. 1997-2242 Page 15
Application No. 08/084,370
failure. Jones further teaches (col. 14, line 60 - col. 15,
line
30) that
After DDA has determined that a drive has failed, it
combines bytes from the remaining three data drives
with the corresponding byte from the parity drive to
regenerate the failed drive's data. These are:
data0fourdrives=data3rdata2rdata1rparity
data0threedrives=data2rdata1rparity
data0twodrives=data1rparity
data1fourdrives=data3rdata2rdata0rparity
data1threedrives=data2rdata0rparity
data1twodrives=data0rparity
data2fourdrives=data3rdata1rdata0rparity
data2threedrives=data1rdata0rparity
data3fourdrives=data2rdata1rdata0rparity
This is done by microcode and data accesses suffer a
slight performance degradation after a drive has
failed.
Data guarding suffers a fairly severe write
performance degradation as partial strip write must
do a read modify write cycle to correctly update the
parity data.
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