Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!brl-adm!adm!rbj@icst-cmr.arpa From: rbj@icst-cmr.arpa (Root Boy Jim) Newsgroups: comp.unix.wizards Subject: A few questions about 4.3BSD partitions and cylinders Message-ID: <11271@brl-adm.ARPA> Date: 14 Jan 88 19:26:15 GMT Sender: news@brl-adm.ARPA Lines: 42 From: Doug Alan This leads me to ask some more questions that have been bugging me for a while. Why is the root partition always 15884 sectors? Where does this number come from? Can you make it bigger or smaller? Will this cause any problems? Why is swap space usually 33440 sectors? Why is For hysterical raisins. I think they come from the gee I'm a tree of the RP06. It just seemed convenient for all root file systems to be the same size, so they can be dd'ed easily. The numbers are not sacred. Any partition can be rounded out to the end of the cylinder easily enuf. For example, an RM03 has is 823 cylinders of five tracks of 32 sectors, giving 160 sector per cylinder. 15884 sectors fills up 99 cylinders and then a few. Since the swap partition starts at cylinder 100, I round out the root partition to 16000 sectors even. This may be done with any and all partitions on SMD disks. To do this, you must edit the partition table in the kernel, or adb it if you don't have source. In 4.3BSD, for example, hp.c contains things like eagle_sizes, rm03_sizes, cdcxxx_sizes, etc, which are arrays of eight structures, containing two ints (or longs, I don't care because all we have is VAXen, SUNs, and a Sequent, where they are both the same). The first int is partition size in sectors, the second is the starting cylinder. You must also edit /etc/disktab as well. Sun (as does Ultrix) contains the partition layout in a label on the disk, so you can do anything you want to with diag (or chpt). Sequent has moved the partition table into the disk configuration file, so even if you don't have source, you can edit them easily. On our Sequent we have two SCSI disks. They seem to have the start specified in sectors, thus wasting no space, so I left them alone. In addition, SCSI geometry is not as important as SMD geometry; I think only formatting programs are supposed to know about it, not ordinary device drivers. (Root Boy) Jim Cottrell National Bureau of Standards Flamer's Hotline: (301) 975-5688 Vote for ME -- I'm well-tapered, half-cocked, ill-conceived and TAX-DEFERRED!