kink@uncle-bens.rice.edu (John R. Deuel) (11/13/89)
I ran into a strange situation this evening and I was wondering if anyone had any clues. All systems involved are running 4.0.3 I had created a large (127Mb) tar file on disk and was going to dump it to tape using dd. The tar file was nfs-mounted on my tapehost, so to my tapehost, I said "dd if=tarfile of=/dev/rmt8 obs=126b" The fileserver with the tarfile on it runs 8 nfsd's, so I figured the worst the load average could get on it was 8. Nope. The server (a 3/280S-24) was at a load of 30 in 3 minutes. The machine literally froze for every task except the serving of the tarfile. If I ^Z'd the dd, life would immediately return to the server. Upon resuming the dd, the machine would vanish again. 1. Why can an NFS client task drive a server with only 8 nfsd's up to a load of 30? 2. Why, even when I nice -15 a process, does it also totally freeze when I run this dd? The nfsd's are running at 0. I understand the priority of processes w/ data coming in from the disk, but shouldn't my process get a chance to run before the nfsd's accept more requests? 3. I've had nfs clients go bonkers before, bombarding a server with requests, but the load has never gone much above the number of nfsd's. Is it just that in the current situation my requests are coming in much faster and slipping inside some scheduling bug window? If anybody has info which might help explain this, I would love to hear it. Please mail to me and I'll summarize to the net, if there's interest. Thanks in advance, John R. Deuel <kink@rice.edu> Systems Programmer, Networking and Computing Systems Rice University, Houston, Texas (713) 527-4013