08-25-2009
the card may be doing its own read ahead and buffering for you, I am not sure enough about the firmware on the PERC card.
I know that in some cases, especially in software RAID, that a read ahead will increase performance in some cases where you were to do some linear reads and such where you read say 4MB ahead of where the target read is, as that will likely be called and you gather the data more efficiently.
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LEARN ABOUT HPUX
nfs2_nra
nfs2_nra(5) File Formats Manual nfs2_nra(5)
NAME
nfs2_nra - control the number of read-ahead operations queued by the NFS version 2 client when sequentially accessing a file
VALUES
Failsafe
Default
Allowed values
Recommended values
A warning will be issued at runtime if the tunable is set to a value greater than 16 since this is beyond the tested limit.
This is not a serious warning but just an information message for the administrator.
DESCRIPTION
controls the number of read-ahead operations that are queued by the NFS version 2 client when sequential access to a file is discovered.
These read-ahead operations increase concurrency and read throughput. Each read-ahead request is generally for 8192 bytes of file data.
Who Is Expected to Change This Tunable?
The distributed file system administrator should examine this value depending on network bandwidth and memory pressure on the client.
Restrictions on Changing
The tunable is dynamic; tuning will take effect immediately on the running system.
When Should the Value of This Tunable Be Raised?
If the network is very high bandwidth and the client and server have sufficient resources, increase this value to more effectively utilize
the available network bandwidth, the client resources, and the server resources.
What Are the Side Effects of Raising the Value?
Tuning incorrectly based on network bandwidth can cause performance problems.
When Should the Value of This Tunable Be Lowered?
In a very low bandwidth network, you might want to decrease this value so the NFS client does not overload the network.
What Are the Side Effects of Lowering the Value?
Tuning incorrectly based on network bandwidth can cause performance problems.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of
HP-UX.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation,
some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tun-
able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was
factory installed on your system, see at
AUTHOR
was developed by Sun Microsystems, Inc.
SEE ALSO
kctune(1M), sam(1M), gettune(2), settune(2), nfs3_nra(5), nfs4_nra(5), values(5).
Tunable Kernel Parameters nfs2_nra(5)