Fujitsu MHV2040AT, MHV2100AT, MHV2080AT Caching operation, Commands that are targets of caching

6.4 Read-ahead Cache

6.4.2 Caching operation

The caching operation is performed only when the commands listed below are received. If any of the following data are stored on the data buffer, the data is sent to the host system.

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All of the sector data that this command processes.

A part of the sector data including the start sector, that this command processes.

If part of the data to be processed is stored on the data buffer, the remaining data is read from disk media and sent to the host system.

(1) Commands that are targets of caching

The commands that are targets of caching are as follows:

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READ SECTOR(s)

READ MULTIPLE

READ DMA

READ SECTOR(s) EXT

READ DMA EXT

READ MULTIPLE EXT

However, if the caching function is prohibited by the SET FEATURES command, the caching operation is not performed.

(2) Data that is a target of caching

The data that is a target of caching are as follows:

1)Read-ahead data that is read from disk media and saved to the data buffer upon completion of execution of a command that is a target of caching.

2)Pre-read data that is read from disk media and saved to the data buffer before execution of a command that is a target of caching.

3)Data required by a command that is a target of caching and has been sent to the host system one. If the sector data requested by the host has not been completely stored in the read cache portion of the buffer, this data does not become a target of caching. Also, if sequential hits occur continuously, the caching-target data required by the host becomes invalid because that data is overwrited by new data.

(3)Invalidating caching-target data

Data that is a target of caching on the data buffer is invalidated under the following conditions:

C141-E218 6-13