NFS Performance Tuning for HP-UX 11.0 and 11i Systems

nfs performance tuning for hp-ux 11.0 and 11i systems page 34

Notes:

Page 34July 22, 2002

How do they work in the WRITE case?

1. Process writes data to buffer cache. If biods are not running, the

writing process sends the data to the server and waits for a reply.

2. If biods are running, the writing process does not block. It continues

writing data to buffer cache while the biods work to drain the buffer

cache, sending data to the NFS server and waiting for replies.

3. While the writing process will not block during the write() system call

(assuming buffer cache space is available), it will block when it

needs to flush, sync, or close the file. In these cases the process

blocks until all data has been successfully written to the server.

biod

GOAL: Keep the client’s buffer cache drained so that when a writing

process flushes a file it only needs to block a short amount of

time while any remaining data is posted to the NFS server

When the client needs to write data to an NFS mounted file, assuming the client is

writing in asynchronous mode (which is the default behavior), the client will write

the data to its local buffer cache. Once the buffer cache data has been written, if

no biod daemons are running then the process writing the data will generate an

NFS write request in its own process context to push the data to the NFS server.

If biods are present then the writing process will post its data to the local buffer

cache and continue writing while the data is sent to the NFS server by a biod.

Several more biods continue to pull data from the client’s buffer cache and send it

to the server, allowing the writing process to continue writing data to buffer cache

as quickly as it can. While the writing process itself will not block during the actual

write() system call, it will block when it needs to flush, sync, or close the file. In

these cases the process sleeps until all data has been written to the server.

Therefore, the goal of the biods in the write case is to drain the client’s buffer cache

so that when the writing process is finished writing and needs to flush, sync, or

close the file, it only needs to block for a short amount of time while any remaining

data is sent to the server.