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

nfs performance tuning for hp-ux 11.0 and 11i systems page 43

Notes:

Page 43July 22, 2002

nfsd

How do they work in the READ case?

1. The nfsd checks the server’s buffer cache for the requested data. If

data is present it’s read from cache and returned to the client.

2. If data is not in the cache the nfsd schedules a READ call to the

underlying filesystem (VxFS, HFS, CDFS, etc.) and sleeps waiting for

the data.

3. When the data arrives it is placed in server’s buffer cache. The

sleeping nfsd process is awoken and sends the data to the client.

GOAL: Retrieve the data requested by the NFS clients from the

server’s buffer cache or physical disks as quickly as possible

When a client system needs to read data from an NFS mounted file, it will first

check its local buffer cache to see if the block of data is already present in cache.

If it is then the read is satisfied without generating an NFS request. If the data is

not present then an NFS READ call will be made to retrieve this data.

When the server receives the READ request it first checks it’s buffer cache to see if

the requested data is already present in it’s cache. If so, it sends the data back to

the client without performing a physical disk I/O.

If the requested data is not present in the server’s buffer cache, the nfsd schedules a

READ from the underlying filesystem (i.e. VxFS, HFS, CDFS, etc.) and blocks

waiting for the disk subsystem to retrieve the data. When the data is returned from

the filesystem it is placed in server’s buffer cache. The sleeping nfsd process is

notified that the data is available. The nfsd retrieves the data from cache and

sends it to the waiting NFS client.