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nfsiod(8)							     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
       Specifies the command path Specifies the file for logging NFS activity

SEE ALSO
       Commands: nfsd(8), nfsstat(8)

       Daemons: async_daemon(2)

								     nfsiod(8)
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