Cached data writing

The z/OS NFS Server always caches writes if out-of-sequence data packets are received or if a physical block of data is partially filled. If the NFS Server is processing in the binary data mode, the writes will remain cached until one of the following occurs: v4 CLOSE occurs, the write timeout for a data set has been reached or, if the logicalcache attribute is defined at less than 2GB, the number of cached packets exceeds the number specified in cachewindow . If the NFS Server is processing text data, the writes remain cached until v4 CLOSE occurs, or the write timeout for a data set occurs. If the logicalcache attribute is defined at less than 2GB and the number of cached packets exceeds the number specified in cachewindow, data processing ends with EIO error code.

The missing data is padded with binary zeroes and record delimiters so that cached writes for text processing are written in the MVS data set on DASD at the location specified in each cached data packet. In the case of cached data packets for binary processing, only binary zeroes will be used to pad the missing data written at the specified location on DASD. See Table 1 .

Attention: It is recommended that the application and NFS client perform the writes in offset and length in multiple of 512 bytes in order to optimize the mapping byte offsets to records process described previously in this section and, therefore, reduce data flush time. On the other hand, for the NFS version 3 commit procedure, the z/OS server will only support committing the cached data when the data set is timed out. For the NFS version 4 commit operation, the z/OS Server will only support committing the cached data upon receiving the close operation.

Table 1. Breakdown of text and binary writes
Description	Binary	Text
Data is flushed to DASD when the	Number of cached packets exceeds the amount specified in cachewindow¹, or the file times out.	File times out. If the number of packets exceeds the amount specified in cachewindow¹, all new out of sequence packets will be dropped.
Padding	Binary zeros	Binary zeros
Record delimiters	There are no record delimiters. Therefore, there is no attempt to add end of line characters.	There can be record delimiters. Therefore, an end of line character is added to the end of the record.

Note:

cachewindow is taken into account when the logicalcache attribute is defined at less than 2GB