US 4,394,733 A · Cache/disk subsystem

Abstract

One or more storage control units (SCUs) interface one or more channels with a plurality of disk drives. One or more host processors are connected to the channels. Associated with the SCUs are one or more cache storage units (CSUs) having a relatively short access time as compared to direct accessing of the disk drives. The CSUs are transparent to the user who programs the hosts as though he were addressing the disk drives directly. An SCU converts the disk address (starting address and number of words to be transferred) to a CSU address and checks a segment descriptor table (SDT) to find out if the segment or segments involved in a transfer are present in a CSU. If so, the data is transferred from the CSU to the channel. If the data is not present in a CSU, then for a read transfer command the data is obtained from the disk drive, entered into the CSU, and supplied to the host. For a write command involving a partial segment, the segment is staged from disk to CSU and the host data overlays the appropriate portion of the segment in CSU without writing the segment back to disk. The post-store method is utilized for destaging to the disk drives segments of data which have been written to while in the CSU.

Claims15

Dependent claims

A data processing system comprising:

a disk drive device for driving a data storage disk;
a host processor for issuing commands defining an operation to be performed and the address of disk space at which said operation is to be performed,
said address specifying the starting address and a number of words of said disk space;
a cache store for storing segments of data;
means for storing a segment descriptor table, said segment descriptor table having an entry corresponding to each segment of data residing in said cache store;
a storage control unit interfacing with said host processor, said disk drive device, said means for storing a segment descriptor table and said cache store;
means in said storage control unit responsive to a command from said host processor calling for a read from said disk for accessing said segment descriptor table to produce a miss signal if a copy of the data from the disk space specified by said command is not resident in said cache store;
means responsive to said miss signal for transferring from said disk space to said cache store the data from the specified disk space which is not resident in said cache store;
and
means in said storage control unit for controlling the transfer of the data at said specified disk space to said host processor;
whereby said host processor may read from said disk any variable number of words of data as specified by said address.

8 more elements

In a data processing system wherein at least one host processor issues commands including function and data addressing information to at least one storage control unit for reading data from or transferring data to at least one disk drive device attached to the storage control unit, the improvement comprising:

a cache store for storing segments of data;
means storing a segment descriptor table, said segment descriptor table having an entry corresponding to each segment of data residing in said cache store;
control means including first means responsive to a command from a host processor calling for a read or a write from or to a disk for accessing said segment descriptor table to produce a hit signal if the segment or segments containing the data specified by said addressing information resides in said cache store, or a miss signal if it does not;
means responsive to said hit signal for transferring the addressed data between said cache store and said host processor through said storage control unit;
means responsive to said miss signal and said addressing information for transferring said addressed data between said disk drive and said host processor through said storage control unit with a copy thereof being entered into said cache store;
said addressing information including the address of a disk drive, a relative word address defining the location on a disk of the first word to be transferred, and the number of words to be transferred, and,
said first means including means for converting said disk drive address, said relative word address and said word transfer length into addressing signals for addressing said cache store.

4 more elements

Dependencies are inferred from the claim text.

Cache/disk subsystem

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Cache/disk subsystem

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Abstract

Claims15