(19) United States
(12) Patent Application Publication (io) Pub. No.: US 2002/0023240 Al
Yamamoto et al. (43) Pub. Date: Feb. 21,2002
(54) STORAGE UNIT SUBSYSTEM
(75) Inventors: Akira Yamamoto, Sagamihara-shi (JP);
Hiroyuki Kitajima, Yokohama-shi (JP);
Kouji Arai, Yokohama-shi (JP);
MATTINGLY, STANGER & MALUR
1800 Diagonal Road
Alexandria, VA 22314 (US)
(73) Assignee: Hitachi, Ltd.
(21) Appl. No.: 09/956,792
(22) Filed: Sep. 21, 2001
Related U.S. Application Data
(63) Continuation of application No. 09/642,815, filed on Aug. 22, 2000, which is a continuation of application No. 09/259,408, filed on Feb. 22, 1999, now Pat. No. 6,145,091, which is a continuation of application No. 08/877,627, filed on Jun. 18, 1997, now Pat. No.
5,917,999, which is a continuation of application No. 07/827,982, filed on Jan. 29, 1992, now Pat. No. 5,682,396.
(30) Foreign Application Priority Data
Jan. 31, 1991 (JP) 03-010574
(51) Int. CI.7 11041. 1/22
(52) U.S. C I 714/6
When receiving a write request from a processor, a control unit checks the condition of existence (or the presence/ absence) in a cache for information necessary for generation of an updated value of a parity record, receives write data and reports the completion of the write request to the processor. In asynchronism with the write request from the processor, the control unit performs a load process for that information among the information necessary for generation of the updated value of the parity record which may be prepared in asynchronism with the write request from the processor and a write after process for the updated value of the parity record.