Browse Prior Art Database

Allocating Storage on Disk Devices

IP.com Disclosure Number: IPCOM000076404D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Birman, A: AUTHOR

Abstract

A method is described for keeping track of available storage space while using disc storage devices. The main ideas incorporated in the method are:

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Allocating Storage on Disk Devices

A method is described for keeping track of available storage space while using disc storage devices. The main ideas incorporated in the method are:

1) A "write" command to the control unit of the device may leave unspecified the address on the device, in which case the device will provide one, the page will be written in it, and the address will be returned to the logical unit which issued the command.

2) In the event that no commands are pending or in process in the control unit or the device, a search is initiated by the control unit for an available "slot". If a location is found, it is stored in a set of registers associated with the device (normally located in the control unit, but possibly in the Main Store).

3) In case a write command is received by the control unit and there are no available slots in the registers, a search is initiated by the device.

Fig. 1 illustrates a modified IBM 3330 facility with 8 disk modules. It is assumed that all records throughout the system have a fixed size called a "page" and the space occupied by a page is called a page "slot". Each page slot on a track is preceded by a count area and a key area in which is stored an "invalid" bit: if the bit is "1" the page is invalid and its storage can be reallocated. If the bit is "0" the page is valid.

In Fig. 1 there are two sets of registers associated with the IBM 3330 facility:
a) The "empty slot" list (ES), which contains pointers to available page slots on devices. b) The "invalidate list" (INV) contains pointers to page slots which have to be invalidated, that is, the invalid bit in their key area has to be set to "1". Clearly, a pointer in INV can be used as such for a write request, or it can be transferred to the ES list after the invalidation execution.

There are three main types of requests to the control unit of this facility:

1) "Read" requests: which specify an address and are directly executed.

2) "Write" requests: normally do not specify a location; an address is provided from INV list, or if empty from ES list. If the ES list is...