Product manual

CDA 7 5630 Product Manual
3-14 77 A1 69UP Rev00
3.2.3.2 Delayed Fast Write
In a delayed fast write operation, CDA 7 cannot store the data in cache until space
in cache becomes available. A delayed fast write condition can only happen if the
cache allocated for writes is currently full with data yet to be "destaged" to the disk
devices. The default cache write ceiling is 80% of the cache.
CONNECT TIME
OVERHEAD
TOTAL SERVICE TIME
DISCONNECT TIME
DELAY
NORMAL
FAST WRITE
Figure 3-12. Delayed Fast Write
Should this situation occur, CDA 7 disconnects the channel directors from the
channels and waits for the disk directors to "destage" the Fast Write data in cache
to disk. When space in cache is available, CDA 7 reconnects the channel directors
to their channels and completes the write operation. CDA 7 continues to process
read operations during delayed fast writes.