NFS Performance

[Todd Lehr]

What is the performance impact of having an application log locally to a file in a local file system directly vs logging to the same file, except referencing the file via a link in an NFS mount.

My view is the impact is minimal since the link redirection is only done when the file is opened.

[Paula J Frazer-Campbell]

Todd

It depend upon how much data is being logged, but what would happen if you went for the NFS option and the remote server died.

I would tend to log locally and ftp the file via a cron job to the remote.


Paula

[Shannon Petry]

NFS efficiency is usually good, but remember that this traffic all adds up. If your on a busy network already, your sure to feel impact unless the writes are rare.

If your writing large amounts of Data, keep it local. If it's output from accounting scripts, etc.. that dont frequently write than no impact at all.

Regards,
Shannon

[Todd Lehr]

Just for clarification, I agree it's better just to log direct to the local file, but this question is aimed at solving a disagreement on root cause.

Also, in this case the logfile is opened and remains open for the duration that the process is running ( Tuxedo ).

Thanks

[Todd Lehr]

Also: 1) In case it wasn't clear, the data is still being written to the local file in the local directory, this question just revolves around how the operating system references the file.

2) I'm not concerned about the NFS server going away, we use ServiceGuard and if that happends I have much bigger problems.

[Krishna Prasad]

There will be some overhead reading the file, however not as painful as the writes which you have local anyway.

Also, to see how much overhead NFS has on your system.

Run Glance and type n - this will show you how much traffic NFS is causing.

Ron

[Sean OB_1]

Todd,

If I read your correctly you are asking what the possible issues are if you log to a file on the local system, but are referencing that file on an NFS mount. And the nfs mount simply is a link to the local file system?

[Sean OB_1]

So the question is will all of the data go through NFS because you reference the local file via an NFS mounted file system?

Or does NFS only get hit on the open, and after that all data goes directly to the local disk?

[Todd Lehr]

Sean: Yes in a way, I believe that the NFS link will get referenced on the open() and then no (or little to none ) NFS traffic will occur until probably another open(). Also, even if process does a open(), write(), close(), the NFS traffic will be limited to pulling the directory entry to re-resolve the link for each open()

thanks

[Vincent Fleming]

Todd,

You are correct. An NFS sym link is just a name. When the OS encounters a sym link, it merely changes the file to be opened to the referenced file.

So, when you open() the sym link name (on NFS or not), it only retrieves the filename that the sym link points to, then that (pointed to) file is opened.

You will cause no more NFS traffic other than the original directory lookup.