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nfsiod(8)


NAME

  nfsiod, biod - The local NFS compatible asynchronous I/O daemon


SYNOPSIS

  nfsiod [numthreads]


DESCRIPTION

  The nfsiod daemon runs on an NFS compatible client machine and spawns
  several IO threads to service asynchronous I/O requests to its server. The
  I/O threads improve performance of both NFS reads and writes.	 Both try to
  enlist the aid of an idle I/O thread. If none is available, the process
  itself issues the request to the server and waits for the reply.

  The optimum number of I/O threads to run depends on many variables, such as
  how quickly the client will be writing, how many files will be accessed
  simultaneously, and the behaviour of the NFS server. For use with a Tru64
  UNIX server, 7 is a good number of I/O threads for most systems.

  When reading, if the client believes the process is reading a file
  sequentially, it requests an I/O thread to read a block ahead of what the
  process is currently requesting.  If the readahead completes before the
  process asks for that block, then the subsequent read system call for that
  data completes immediately and does not have to wait for the NFS request to
  complete.  Read ahead will be triggered again so the read may find that
  next block available as well.

  When writing a file, the client takes the process's data, passes the
  request to an I/O thread and immediately returns to the process.  If the
  process is writing data faster than the network or server can process, then
  eventually all the I/O threads become busy and the process has to handle a
  NFS write itself. This means the process has to wait until the server
  finishes the write.  For Tru64 UNIX servers, the NFS block size is 8Kb and
  UFS tries to cluster I/O 64Kbs at a time.  If the client is running with 7
  I/O threads, 8 write requests can be in progress at once.  This allows the
  client and server to write data 64Kbs at a time and is the reason for
  recommending 7 I/O threads.

  Unlike nfsd, each client thread can use either UDP or TCP.  However, if TCP
  mounts are active, the nfsiod process will time out, close idle TCP
  connections, and acknowledge any connections closed by the server.

  The nfsiod process is also responsible for syncing the access time and
  modify times for special files and named pipes (fifos).  Because I/O to
  these files does not go through the NFS server, NFS clients have to
  directly update the access time and modify time attributes.

  The client threads are implemented as kernel threads; they are part of
  Process ID 0, not the nfsiod process.	 The ps axml command displays idle
  I/O threads under PID 0.  Idle threads will be waiting on nfsiod_wait.
  Therefore, if 7 I/O threads are configured, only 1 nfsiod process is
  displayed in the output from the ps command, although 7 client threads are
  available to handle NFS requests.


FILES

  /usr/sbin/nfsiod
      Specifies the command path

  /var/adm/syslog/kern.log
      Specifies the file for logging NFS activity


SEE ALSO

  Commands: nfsd(8), nfsstat(8)

  Daemons: async_daemon(2)

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