From iiitac@swan.pyr Fri Jan 21 15:47:48 EST 1994 Article: 4541 of comp.os.linux.development Newsgroups: comp.os.linux.development Path: bigblue.oit.unc.edu!concert!news-feed-1.peachnet.edu!emory!europa.eng.gtefsd.com!howland.reston.ans.net!pipex!uknet!cf-cm!cybaswan!iiitac From: iiitac@swan.pyr (Alan Cox) Subject: Re: nfs performance Message-ID: <1994Jan21.172349.12742@swan.pyr> Organization: Swansea University College References: <758962807.0@freudsys.iaf> Date: Fri, 21 Jan 1994 17:23:49 GMT Lines: 90 Sounds like we need an NFS FAQ Lets try a first draft - maybe this can be hacked onto a net howto or something Q1. Files get corrupted when using NFS over wider area networks or SLIP Certain vendors (Sun primarily) shipped many machines running NFS without UDP checksums. Great on ethernet, suicide otherwise. UDP checksums can be enabled on most file servers. Linux has it enabled by default from pl13 onwards - but both ends need to have it enabled... Q2. My NFS files are all read only The Linux NFS server defaults to read only. RTFM the 'exports' and nfsd manual pages. With non Linux servers you may also need to alter /etc/exports Q3. I mount from a linux nfs server and while ls works I can't read or write files. You must mount a Linux filestore with rsize=1024,wsize=1024 (or 2048 if you really want - 1024 is a better choice). Q4. I mount from a linux nfs server with a blocksize of between 3500-4000 and it crashes the Linux box regularly I know good isn't it [NOT]. Basically don't do it then. (see Q3). Q5. Can Linux do NFS over TCP No. If someone wanted to spend the time and update the rpc code to add rpc stream record marking it should work then. Q6. I get loads of strange errors trying to mount a machine from a Linux box. Make sure your users are in 8 groups or less. Older servers require this. Q7. Linux NFS clients are very slow when writing to Sun & BSD systems NFS writes are normally synchronous (you can disable this if you don't mind risking losing data). Worse still BSD derived kernels tend to be unable to work in small blocks. Thus when you write 4K of data from a Linux box in the 1K packets it uses BSD does this read 4K page alter 1K write 4K back to physical disk read 4K page alter 1K write 4K page back to physical disk etc.. Better systems don't have this problem. The Linux client is however quite slow anyway. Q8. I've heard NFS is not secure is this true Yes, totally. Running NFS in an uncontrolled environment is rather like leaving your front door open, painting 'On holiday' on your house and posting maps to every known criminal... In a fairly secure environment or when you can recover data from stupid misuse its pretty much OK. The worst someone can easily do is alter all the files on an NFS mounted disk and/or crash the machine. So long as you don't mount your system files writable you should be vaguely safe Q9. I occasionally mount from lots of different places do I have to set the all mounted each boot. No you can use the automounter to mount disks as you access them. Q10. How do I stop things hanging when a server goes down There are three main NFS behaviours soft: Your NFS client will report an error to the process concerned if an NFS server doesn't answer after a few retries. Most software handles this well - but not all. hard: Your NFS client will try forever unless killed off. Operations will be restarted when the NFS server recovers or reboots. hard,intr: As hard but ^C will also stop the NFS retrying. In a few cases - notably nfs mounted /usr/spool/mail disks this doesn't help as the shell will be ignoring ^C when it checks you have mail...