ICKDSF MANUAL PDF

IBM quickly replaced the with the faster and larger Subsequently, the feature set was implemented on the family of storage controls and an integrated attachment of the System Model The following example of a channel program [19] reads a disk record identified by a Key field. The track containing the record and the desired value of the key is known. The SCU will search the track to find the requested record. The actual number of subchannels provided depends upon the system model and its configuration.

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IBM quickly replaced the with the faster and larger Subsequently, the feature set was implemented on the family of storage controls and an integrated attachment of the System Model The following example of a channel program [19] reads a disk record identified by a Key field. The track containing the record and the desired value of the key is known. The SCU will search the track to find the requested record. The actual number of subchannels provided depends upon the system model and its configuration.

RPS permits channel disconnection during most of the rotational delay period and thus contributes to increased channel utilization. The control unit implements RPS by dividing each track into equal angular segments. With a block multiplexer channel the channel is free during the time the DASD is seeking and again while the disk rotates to beginning of the track.

A selector channel would be busy for the entire duration of this sample program. Defect skipping[ edit ] Defect skipping allows data to be written before and after one of more surface defects [l] allowing all of a track to be used except for that portion that has the defect. This also eliminates the time that was formerly required to seek to an alternate track. Defect skipping was introduced in with the attached via the Model 2 Storage Control Unit [22] or integrated attachments on small systems.

Defect skipping was essentially a factory only feature until when CCWs for management along with associated utilities were released. The dynamic path selection function controls operation of the two controllers, including simultaneous data transfer over the two paths.

When supported by the operating system, each controller can serve as an alternate path in the event the other controller is unavailable. Once a path group for a device has been established, it may be accessed over any path which is a member of the group to which it is reserved. In addition, on XA systems which set the multipath mode bit in the function control byte byte 0 to a 1, block multiplex reconnections will occur on the first available path which is a member of the group over which the channel program was initiated regardless of the reservation state of the device.

Channel programs can be executed such that channel and storage control activities required to end execution of one command and advance to the next do not have to occur during the inter-record gap between two adjacent fields. An intermediate buffer in the storage control allows independent operations between the channel and the device.

A major advantage of ECKDs is far longer cables; depending upon application it may improve performance. A large memory in the Director, the cache, is divided into track slots that store data from the tracks. A smaller area is a directory that contains entries that allow data to be located in the cache. For example: Unconditional Reserve allowed the releasing a device reserved to another channel and reserving the device to the channel issuing the command.

Read Multiple Count Key Data could more efficiently read full tracks allowing for more efficient backups. Originally CKD records had a one-to-one correspondence to a physical track of a DASD device; however over time the records have become more and more virtualized such that in a modern IBM mainframe there is no longer a direct correspondence between the a CKD record ID and a physical layout of a track.

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For a detailed description and examples of each command, see:. If more than one step name majual specified, the entire namelist must be enclosed in parentheses. This is acceptable for private volumes, such as tape or mountable DASD volumes, but unacceptable public volumes. It is also used for renaming and scratching deleting a data set. This page was ickdf edited on 21 Novemberat Produces a report showing the assignment of primary blocks to alternate blocks on FBA devices.

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Count key data

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ICKDSF commands

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