Delayed initiation of read-modify-write parity operations in a r

Details Delayed initiation of read-modify-write parity operations in a r Delayed initiation of read-modify-write parity operations in a r

1992-10-23

1995-02-07

Canney, Vincent P.

Excavating

371 102, G06F 1100

Patent

active

053881087

ABSTRACT:
An improved method for updating data and parity information in a RAID level 4 or 5 disk array employing a read-modify-write (RMW) process for updating data and parity information. During normal RMW operations, the old data and old parity information to be updated are read from disk, new parity is generated, and the new parity information and new data written to disk. The improved RMW method separates the execution of data read and write operations from the execution of parity read, generation and write operations to permit greater efficiency in the utilization of the drives within the array. The method identifies the disk drives containing the data and parity to be updated and places the proper read and write requests into the I/O queues for the identified data and parity drives, scheduling parity operations; i.e. reading old parity information from the parity drive, generating new parity information and writing the new parity information to the parity drive; for execution when best accommodated in the I/O queue for the parity drive, following the read of old data from the data drive.

REFERENCES:
patent: 4884271 (1989-11-01), Concha et al.
patent: 4914656 (1990-04-01), Dunphy, Jr. et al.
patent: 5257362 (1993-10-01), Menon
patent: 5265098 (1993-11-01), Mattson et al.
"A Case for Redundant Arrays of Inexpensive Disks (Raid)" by David Patterson et al. ACM Cont., Chicago Ill. Jun. 1988.
Disk Arrays Explained by Roger C. Alford, Oct. 1992 issue of Byte magazine.

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