Restarting a failed data transfer

About this task

FTP supports two subcommands for restarting data transfers that fail. Select the appropriate subcommand based on the data transfer mode at the time the data transfer failed.

If stream mode data transfer was used, use the srestart subcommand to restart the data transfer. See SRestart subcommand—Restart a stream data transfer for a description of stream mode restart.
If block or compressed mode was used, use the restart subcommand to restart the data transfer. See REStart subcommand—Restart a checkpointed data transfer for a description of block or compressed mode restart.

To restart a block or compressed mode data transfer, checkpointing must have been initiated prior to the start of the transfer. You can use either the LOCSITE or SITE subcommands to initiate checkpointing.

The LOCSITE subcommand parameter CHKPTINT controls the checkpoint interval at the client, and the parameters CHKPTPREFIX and RESTGET control the naming of the client checkpoint data set.
The SITE subcommand parameters CHKPTINT and RESTPUT control the checkpoint and restart processing at the server.

Each of the LOCSITE/SITE parameters is also supported in the FTP.DATA file.

If the local file or the remote file is a z/OS® UNIX named pipe, do not use the srestart or restart subcommands to restart the file transfer. If the transfer type is binary and the local file is the named pipe, you can resume the transfer using the restart instructions below, or you can use the instructions below to start the transfer again. If the transfer type is not binary, or if the remote file is the named pipe, you must start the transfer again.

Procedure

To start the transfer again:
- If you are trying to restart a file transfer into a named pipe, use these steps to restart it:
  1. Stop the named pipe reader, directing it to discard the data it has received so far.
  2. Empty the named pipe. This prevents FTP from appending to any residual data in the named pipe.
  3. Restart the named pipe reader.
  4. Repeat the original file transfer subcommand.
- If you are trying to restart a file transfer from a named pipe, use these steps to restart it:
  1. Stop the named pipe writer.
  2. Empty the named pipe. This prevents the named pipe writer from appending to any residual data in the named pipe.
  3. Restart the named pipe writer, having it re-create the data stream.
  4. Issue the original file transfer subcommand.
To restart the file transfer (for binary transfers only):
- If you were trying to restart a transfer into a named pipe in the FTP client file system, take these steps to resume the file transfer:
  1. Figure out the number of bytes, bytes, the named pipe reader on the FTP client host read from the named pipe.
  2. Ensure that the named pipe is empty.
  3. From the z/OS FTP client, issue QUOTE REST bytes to direct the server to start the next file transfer from offset bytes into the server file.
  4. Issue the original file transfer subcommand.
  Note: The z/OS FTP server supports the REST command in stream mode only when EXTENSIONS REST_STREAM is coded in the server FTP.DATA.
- If you were trying to restart a transfer from a named pipe in the FTP client file system, follow these steps to resume the file transfer:
  1. Do one of the following from the FTP client to learn the number of bytes, bytes, stored in the server file:
    - Issue the DIr subcommand
    - Issue the LS -l subcommand
    - Issue QUOTE SIZE serverfile
  2. Ensure that the named pipe is empty.
  3. Restart your named pipe writer, telling it to regenerate the data starting from point bytes.
  4. Issue the APpend subcommand to append the named pipe to the server file.
  Note: The z/OS FTP server supports the SIZE command only for regular z/OS UNIX files, and only when the EXTENSIONS SIZE statement is coded in the server FTP.DATA.