Method and means for fast writing data to LRU cached based DASD arrays under ...

FREE POOL

DATA CACHE

PARITY CACHE

BUFFER POOL

data from CPU 1 placed in 2 buffer locations

FIG. 4'A

FREE POOL
DATA CACHE
PARITY CACHE
BUFFER POOL

data logically moved to cache - send "done" msg to CPU

FIG. 4B

old d may reside d

d

old P may reside
here

old d, old P, if not already in cache
and new P

FREE POOL
DATA CACHE
PARITY CACHE
BUFFER POOL

FIG. 4C

DATA LOSS SITUATION

- Hard memory error while writing new P from loc Y

- Cannot read one of blocks D2, D3, .. D6

MODERATE ROBUST DESTAGE STEPS

FIG. 6

NO DATA LOSS IF ALL WRITES AFTER ALL READS DONE

HIGHLY ROBUST DESTAGE STEPS

FIG. 7

Destage Entire Parity Group

blocks in cache land NVS —^

DT D2' D3' D4' D5' D6' j D1' D2* D3' D4' D5' D6'

D1 D2 D3 D4 D5 D6 P

^ DASD array blocks

Destage Part of Group; all blocks in cache

i
i

Df D2' D3 D4 D5 D6 j DV D2'

D1-D2 D3 D4 D5 D6 P

Destage Part of Group; stage in missing blocks

i
i

Df D2' D3 D4 D5 D6 j Df D2'

D1 D2 D3 D4 D5 D6 P

Destage Part of Group; read old data and parity

i
i

Df D2' | D1' D2'

D1 D2 D3 D4 D5 D6 P

ASPECTS OF DESTAGING PARITY GROUP

FIG. 8