Date: Fri, 18 Nov 2005 09:55:34 -0500 (EST) From: Daniel Ellard <ellard@eecs.harvard.edu> To: freebsd-hackers@freebsd.org Subject: Re: Filesystem monitoring question Message-ID: <20051118094225.E72964@bowser.eecs.harvard.edu> In-Reply-To: <20051118120039.BB3EE16A421@hub.freebsd.org> References: <20051118120039.BB3EE16A421@hub.freebsd.org>
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There are many possible answers to this question. Can you explain more about exactly what you need? Depending on what you can and cannot access, one method is to sniff the network or the network interface. This will tell you when write requests come to the server, but can require a great deal of careful bookkeeping to know which write was to what file, etc. And it also doesn't tell you what the file system is doing, because these writes might be delayed/clustered/die in the cache. But it's a technique you can do on a machine for which you don't even have a login. If you were on Solaris, the answer is DTrace. But then you wouldn't be posting to this group... IIRC some of folks at SUNY Stony Brook (Erez Zadok's students, I think) have a VFS shim that traces calls through the VFS layer. If everything you're doing goes through VFS, that would work. But if it's a production server, you might not be able to get permission to fiddle with the kernel. ktrace might do everything you need, but I understand that it has an impact on system performance under load. I don't know if that matters to you at all. It also might be awkward if the SMB and NFS servers are kernel processes. (I just don't know; I've only used ktrace on ordinary user-land processes, and not even much of that.) -Dan
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