File-writing parameters

• output_devices (list of strings).

  This is a list of devices (or filesystems) on the L1 server which can be written to independently. Each output_device is identified by a pathname (usually the mount point of a filesystem) such as "/ssd" or "/frb-archiver1". Each output_device will get a separate I/O thread.

  When the L1 server needs to write a file, it looks for a “matching” output_device whose identifying pathname is a prefix of the filename being written. For example, the output_device /ssd would match the filename /ssd/dir/file. The file will then be queued for writing by the appropriate I/O thread.

  In subscale testing on a laptop, I usually set output_devices: [""], which creates one output_device which matches all filenames, and a single I/O thread to process all write requests.

  On the real nodes, I usually set:

  output_devices: [ "/ssd", "/frb-archiver-1", "/frb-archiver-2",
                    "/frb-archiver-3", "/frb-archiver-4" ]
  

  which defines 5 file I/O threads, corresponding to (4 NIC’s) + (1 SSD) in the node. Recall that the L1 node is configured so that it “thinks” the NFS server is four different servers, mounted on directories /frb-archiver1, /frb-archiver2, /frb-archiver3, /frb-archiver4. File writes to each of these four filesystems will be sent from the corresponding NIC.

  Note that output_devices: [ ] (an empty list) means that the server spawns no I/O threads and all write_requests fail, whereas output_devices: [""] means that the server spawns one I/O thread which matches every write request.

If the following parameters are defined, then the node will continuously stream all incoming data to either its local SSD or NFS.

• stream_acqname (string, optional).

  If this parameter is specified, then the node will continuously stream all incoming data to either its local SSD or NFS. Warning: it’s very easy to use a lot of disk space this way!

  The ‘string_acqname’ parameter is a unique identifying directory name for the acqisition. If the given acquisition already exists (probably from a previous run) then the L1 server will abort.

• stream_devname (string, optional).

  Either "ssd" (the default) or "nfs".

  NFS bandwidth is limited, so if you’re writing to NFS then you probably want to reduce the number of beam_ids, by assigning a value to ‘stream_beam_ids’ (see below).

• stream_beam_ids (list of integers, optional).

  A list of beam_ids to stream to disk.

  Must be a subset of ‘beam_ids’, the set of all beam_ids processed by the server. If unspecified, every beam_id processed by the server will be streamed.