nfsiod(8)nfsiod(8)NAME
nfsiod, biod - The local NFS compatible asynchronous I/O daemon
SYNOPSISnfsiod [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)