NFS Monitoring


As of version 3.2.1, nfs monitoring has undergone a major change. Unlike the old behavior which only reported on the client or server for a specific version, by default nfs reporting now collects data for all types of nfs data including nfs version 4. This also means when reporting nfs summary data, all statistics are aggregated in both brief and summary formats.

A system typically runs one version of NFS and usually acts as a client or server and so by aggregating the data the numbers being reported in brief mode will already be for a single type of data. Furthermore, in verbose mode the client/server data are broken out so even if the system is acting as both a client and server you will be able to differentiate the data being reported.

As an optimization as well as a convenience, collectl looks at the raw read/write fields for each set of nfs data, which represent the totals since boot. If those fields are both 0, it is assumed there is no nfs activity and the rest of the statistics will also assumed to be zero. With the excepion of the detail format descripted later, this all happens behind the scenes. However, just because those fields are non-zero does not mean there is currently nfs activity. In fact if you mount a filesystem, write to it and dismount it, those counters will remain non-zero until the system is rebooted. In other words, this approach is not perfect but simply provided as a mechanism to help reduce the need for user-specified filters to help focus the detail output.

Data Filtering

As they say, your mileage may vary and if your system is running mixed nfs versions and/or acting as a client and server and you really only want a subset of the activity included in the summary or detail reports, you can modify the behavior by specifying one or more filters with the --nfsfilt switch. If you just select clients, only data for those clients will be included in brief, summary and detail formats. However, if recording to a raw file, collectl will record data for all NFS client versions even if you've only selected one or two. The same holds true for servers. When you do use -nfsfilt, those values are display in the brief and verbose headers both during collection and playback.

Detail Data

The data collected for NFS V2 and V3 is quiet similar in that V3 reports of superset of what V2 reports with the exception of root and wrcache. V4 reports a lot more counters than either but many of the same key ones as V3 and so the detail format has been standardized on the V3 counters. In this mode, one line is reported for each of the 6 types, with blank entries for the non-common fields as shown here. Note that only rows for those types determined to be active by checking the read/write fields or explicitly selected through filters, will be included:
#Type Read Writ Comm Look Accs Gttr Sttr Rdir Cre8 Rmov Rnam Link Rlnk Null Syml Mkdr Rmdr Fsta Finf Path Mknd Rdr+
 Clt2    0    0         0         0    0    0    0    0    0    0    0    0    0    0    0    0
 Svr2    0    0         0         0    0    0    0    0    0    0    0    0    0    0    0    0
 Clt3    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0
 Svr3    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0
 Clt4    0    0    0    0    0    0    0    0    0    0    0    0    0    0    0                   0    0
 Svr4    0    0    0    0    0    0    0    0    0    0    0    0    0

Looking at detail data for more than one type of data can be difficult to watch. Consider using --home which can give the feel of a real-time display in top format.

Playing back data generated by older versions of collectl

Collectl is smart enough to do the right thing. In other words if you're playing back data generated by a pre-3.2.1 version of collectl, collectl figures out what type of data the file contains and actually sets --nfsfilt for you (in fact it won't let you select it yourself) and only displays the type of data in the file.

Playing back newer data with older versions of collectl

Any raw file created by Version 3.2.1 or greater records nfs data in a format that will not be recognized by earlier versions of collectl and any attempts to read it will result in fields of all zeros. It is not expected that this would typically happen but as they say, it is being stated here for completeness.
updated June 26, 2009