Path: utzoo!utgpu!water!watmath!clyde!rutgers!mit-eddie!bloom-beacon!athena.mit.edu!nessus From: nessus@athena.mit.edu (Doug Alan) Newsgroups: comp.unix.wizards Subject: A few questions about 4.3BSD partitions and cylinders Message-ID: <2199@bloom-beacon.MIT.EDU> Date: 9 Jan 88 08:53:10 GMT Sender: daemon@bloom-beacon.MIT.EDU Reply-To: nessus@athena.mit.edu (Doug Alan) Organization: Kate Bush and Butthole Surfers Fandom Center Lines: 55 Hi. I have some questions about partitions and cylinder groups in 4.3BSD that I hope someone might be able to answer. If you can help enlighten me, and feel your answer is worth a posting, please also mail it to me, as I do not always keep up with netnews. We have some uVaxes here where I work that have Fujitsu M2246E drives controlled by Sigma SCD-RQD11-EC controllers. The controller is a little bit unusual, however, in that it reserves the first track for its own use, and what you see when talking to the controller as sector 0 of the disk is really sector 35. Now I believe that 4.3BSD wants partitions to begin at the beginning cylinders. What happens if they do not begin at the beginning of a cylinder? I know that everything still works, but is there a big performance loss? How much? Clearly there's not much I can do about the root partition not beginning on a cylinder boundary with this Sigma controller, but should I adjust the partition offsets of other partitions so that they begin on cylinder boundaries? Moving to a different but related circumstance, where I used to work, at Project Athena, we had zillions of workstations, and we had an installation software kit that would set up new workstations which had just been removed from the box. The install kit would initialize file systems on the disk drive of a workstation and load the file systems up with software. It was possible for the installation kit to determine the size of the disk drive (we were using Ultrix which lets you easily determine the size of a disk drive), but it wasn't easy for the kit to determine what kind of disk drive the drive was, so when the installation software ran "newfs", it told "newfs" that the drive was an RD52 (though it used the "-s" option to adjust the size), no matter what kind of drive was actually on the workstation. Thus if the workstation had an RD53 or RD54 the fine-tuning parameters of the file systems on the drive were set as if the drive were an RD52. What kind of performance loss does this sort of thing cause? 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 there often empty space inbetween partitions. I can understand why there would be empty space between the root partion and the swap partition if the root partition has to be 15884 sectors and the swap partition should begin on a cylinder boundary, but this doesn't explain why there is empty space between other partitions. For example, I'm looking now at the partition table for an RA80. The E partition ends at sector 121904 but the F partition doesn't begin until 121954. Is there any important reason that 50 sectors have been left unused? |>ouglas /\lan Software/Hardware Analyst Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology (or nessus@athena.mit.edu nessus@mit-eddie.uucp)