A RAID disk array controller [(FIG. 7)] implements a write mask 16
to
support partial-stripe updates [(FIG. 4)] from a host system [60]
without expensive RAM to RAM copying and repeated disk accesses to assemble the
updated stripe. New data from the host [20,22] is transferred into a single
buffer [14,40] and a local processor [80] tracksby setting
bits [30,32] in the write maskwhich segments of the target stripe
are updated. The disk array is accessed to transfer the target stripe into the
same buffer [40], but the buffer memory write enable [58] is inhibitedresponsive
to the write mask [52]during transfer of the segments that were
updated by the host. The complete, updated stripe is thus formed in a single buffer
for parity calculations and write to the disk array.
