Date: Sun, 20 Aug 95 13:40:33 MDT From: terry@cs.weber.edu (Terry Lambert) To: dima@bog.msu.su (Dmitry Khrustalev) Cc: hackers@freefall.FreeBSD.org Subject: Re: Making a FreeBSD NFS server Message-ID: <9508201940.AA22999@cs.weber.edu> In-Reply-To: <Pine.SOL.3.91.950820080008.552A-100000@sunny.bog.msu.su> from "Dmitry Khrustalev" at Aug 20, 95 09:04:04 am
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> > You can turn on async writes in the BSD NFS server. > > > > Be warned that, though Sun and SVR4 do this too, this is a cache > > coherency violation and can result in Bad Things Happening in case > > of a server power failure or other failure that results in the > > server going down, then coming back up while the app on a client > > is still running. This is because the client will think the data > > was written and may depend on being able to retrieve it later > > (ie: a database index). > > Wrong, Sun had never included a method for enabling async writes in their os. > ( other than adb, anyway). Ditto SVR4. SGI ships their boxes with async > writes turned on by default, their reasoning is that every server is > protected by UPS. Green and white NetWork Administration Manual, about bage 128? I remember it was a nice binary page number... It's a debug statement you put in /etc/rc, and it was there by default the last time I looked at the Solaris systems I use. I'm not the only one with root, though, so I could be mistaken. I think it gets added at the same time as the "security fix" to disallow subdir mounts. > No, NFSv3 does not include cache coherency protocol. > > Quoting v3 rfc: > > Neither the NFS version 2 protocol nor the NFS version 3 > protocol provide a means of maintaining strict client-server > consistency (and, by implication, consistency across client > caches). > > What it does is implement is *safe* async writes. Ah, Okie-doke. I thought I remembered it from the Sun draft paper of over a year and a half ago. > > Since I *don't* want everyone going of and tweaking their systems > > for async NFS writes unless they are *deadly* serious, you can dig > > the information out of the docs and sources yourself. Correct my previous post to say "don't enable async writes, ever, it's not worth it (unless you have a UPS on your server). Terry Lambert terry@cs.weber.edu --- Any opinions in this posting are my own and not those of my present or previous employers.
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