Date: Sun, 06 Nov 2011 14:11:33 +0100 From: "Ronald Klop" <ronald-freebsd8@klop.yi.org> To: freebsd-fs@freebsd.org, "Rick Macklem" <rmacklem@uoguelph.ca> Cc: Josh Paetzel <jpaetzel@freebsd.org>, zkirsch@freebsd.org Subject: Re: [RFC] Should vfs.nfsrv.async be implemented for new NFS server? Message-ID: <op.v4iz9jic8527sy@212-182-167-131.ip.telfort.nl> In-Reply-To: <1558351773.1229453.1320542285788.JavaMail.root@erie.cs.uoguelph.ca> References: <1558351773.1229453.1320542285788.JavaMail.root@erie.cs.uoguelph.ca>
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On Sun, 06 Nov 2011 02:18:05 +0100, Rick Macklem <rmacklem@uoguelph.ca> =20 wrote: > Hi, > > Josh Paetzel pointed out that vfs.nfsrv.async doesn't exist > for the new NFS server. > > I don't think I had spotted this before, but when I looked I > saw that, when vfs.nfsrv.async is set non-zero in the old server, > it returns FILESYNC (which means the write has been committed to > non-volatile storage) even when it hasn't actually done that. > > This can improve performance, but has some negative implications: > - If the server crashes before the write is committed to > non-volatile storage, the file modification will be lost. > (When a server replies UNSTABLE to a write, the client holds > onto the data in its cache and does the write again if the > server crashes/reboots before the client does a Commit RPC > for the file. However, a reply of FILESYNC tells the client > it can forget about the write, because it is done.) > - Because of the above, replying FILESYNC when the data is not > yet committed to non-volatile (also referred to as stable) > storage, this is a violation of RFC1813. Just out of curiosity. Why would lying about FILESYNC improve performance= =20 over UNSTABLE? The server does the same work. Only the client holds data = =20 longer in memory. I only see impact if the client has just a little bit o= f =20 memory. Ronald.
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