Date: Tue, 21 Apr 1998 23:33:44 +1000 From: Stephen McKay <syssgm@dtir.qld.gov.au> To: Mattias Pantzare <pantzer@ludd.luth.se> Cc: freebsd-stable@FreeBSD.ORG, syssgm@dtir.qld.gov.au Subject: Re: make buildworld over NFS Message-ID: <199804211333.XAA12764@troll.dtir.qld.gov.au> In-Reply-To: <199804211257.OAA28387@zed.ludd.luth.se> from Mattias Pantzare at "Tue, 21 Apr 1998 14:57:51 %2B0200" References: <199804211257.OAA28387@zed.ludd.luth.se>
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On Tuesday, 21st April 1998, Mattias Pantzare wrote: >> BTW, I use hard mounts, not soft. It's a bad idea to use soft except with >> read-only mounts. > >Why? Nobody explains it much: To quote from the Solaris mount_nfs page "File systems that are mounted read-write or that contain executable files should always be mounted with the hard option. Applications using soft mounted file systems may incur unexpected I/O errors." And Digital Unix offers: "File systems that are mounted rw (read-write) should use the hard option", which is just ripped off from SunOS. But it's really quite simple: soft mounts are allowed to return errors after a certain number of timeouts. So your programs will fail when the server goes down or temporarily is hard to reach. Hard mounts must retry until doomsday. So, in theory, the writes will complete when the server comes back up, even if it is next year. Same deal for executables running off NFS. Hard mounts should just block the process until the server comes back. Soft mounts will let them die if they need some new text pages and the server is unavailable. Also, nfsiod is doing write-behind for you, so you probably could lose writes without your programs even noticing if the server drops out then returns. I just made the mistake of trying to verify this by reading the code. Oh, my head! Stephen. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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