I'd be curious to see if this is a function of how NetApp handles NFS, or if it's deeper than that. I'd like to try this out on a bog-standard ext4 fs and see if the behavior's still the same. Likewise for the native Linux NFS server.
John On 12/04/2013 10:37 PM, Alex Aminoff wrote: > On 12/4/2013 10:21 PM, Matt Simmons wrote: >> My knowledge is somewhat limited to the Linux world, but in my >> experience I've never seen a mount be set to 'ro' and have anything >> updated. I hate to use the term 'flabbergasted', but I'm pretty sure >> that if I saw an implementation that didn't respect the 'ro' flag, I'd >> be at the very least 'put out', and perhaps even vitriolic. >> > Yeah, flabbergasted is a good description of how I felt. > > Nevertheless, I tested it and unless I messed up my test, an NFS mount > with -o ro, you read a file on the mounted FS, and the access time is > updated. > > For the test the server was a NetApp, the client was Linux. > > There is a mount flag -o noatime that does what I want. But I would > argue that this is not right. The simplest behavior - nothing is ever > written period - should be what you get by default, and then there could > be a flag that enables exceptional behavior, that is updating the access > time. > > I can squint and see why it would be the way it is. One perspective is > that the naive assumption is that reading off a RO filesystem should be > just like reading any other way; when you read, the OS conveniently > remembers when you did. The inconsistency of "writing" to a read-only > thing is less important than the inconsistency of not updating the > access time when the file is read. > > But what if the underlying device is not capable of recording access > times, like a CD-ROM? Can you look at the mount options and see that a > CDROM is read-only? But then you can't know whether access times will be > updated unless you use some other method to find out what the underlying > device is. So that's an abstraction violation. Bother, I don't have a > unix box easily to hand where I can check what the mount options on a > CDROM look like. > > I'm not sure if this is just grousing, or flame bait, or a gotcha that > every sysadmin should know because there is no way to anticipate it. > > - Alex > >> --Matt >> >> >> >> On Tue, Dec 3, 2013 at 2:21 PM, Alex Aminoff <[email protected] >> <mailto:[email protected]>> wrote: >> >> >> Hi folks. I encountered something odd. >> >> Suppose you mount a file system read only. You read a file from >> it. Does >> the access time of that file get updated? >> >> In one place I found documentation saying no. But other places seem to >> imply that it does. >> >> Does the answer change if it is an NFS mount? >> >> I have deliberately left details of what OS I'm using out, because it >> seems to me that the answer should be consistent, and if it is not, it >> should be documented publicly. >> >> - Alex Aminoff >> BaseSpace.net, NBER >> >> >> >> >> _______________________________________________ >> bblisa mailing list >> [email protected] <mailto:[email protected]> >> http://www.bblisa.org/mailman/listinfo/bblisa >> >> >> >> >> -- >> "Today, vegetables... Tomorrow, the world!" >> >> >> _______________________________________________ >> bblisa mailing list >> [email protected] >> http://www.bblisa.org/mailman/listinfo/bblisa > > _______________________________________________ > bblisa mailing list > [email protected] > http://www.bblisa.org/mailman/listinfo/bblisa > _______________________________________________ bblisa mailing list [email protected] http://www.bblisa.org/mailman/listinfo/bblisa
