Return to BSD News archive
Path: sserve!newshost.anu.edu.au!munnari.oz.au!ariel.ucs.unimelb.EDU.AU!ucsvc.ucs.unimelb.edu.au!lugb!latcs1!wongm Newsgroups: comp.os.386bsd.questions Subject: Re: Disklabel vs. DOS partition table Message-ID: <CF81LG.3F4@latcs1.lat.oz.au> From: wongm@latcs1.lat.oz.au (M.C. Wong) Date: Thu, 21 Oct 1993 00:34:27 GMT References: <1993Oct19.145248.22328@alw.nih.gov> <BINWU.93Oct19181017@poisson.EECS.Berkeley.EDU> Organization: Comp Sci, La Trobe Uni, Australia Lines: 83 In article <BINWU.93Oct19181017@poisson.EECS.Berkeley.EDU> binwu@poisson.EECS.Berkeley.EDU (Bin Wu) writes: >In article <1993Oct19.145248.22328@alw.nih.gov> crtb@helix.nih.gov (Chuck Bacon) writes: > > I've seen numerous posts complaining that the DOS or the BSD > filesystem got zapped, either by FDISK or by disklabel. > Having just lost both a DOS and a BSD partition while trying > to get pcfs to mount, I'd like to get straightened out! >Having hosed and *recovered* a dos disk myself, I can certainly relate >the frustration you run into. I had to buy a book on PC hard disks and >read several chapters before I could understand what I did and how to >recover. :) Can you please kindly recommend the book you are talking about ? Or if someone out there knows of such a book, please can u recommend it to me. I think the internal details of all those different disk types are as bad a black art as the design of computer cache. > > Question 1: > What is the relation between the DOS partition table's location > (the very first sector on the disk, I think) and that of the > disklabel? I.e., where does the disk label get written? > >Dos partition table(or master boot record, mbr) is the first sector on >disk, you need it no matter what operation system(s) you run. The >disklabel on the other hand, appears on the 2nd sector of you 386BSD >partition (the 1st sector is /usr/mdec/wdboot, and the rest is bootwd, >all together totals 16 sectors). > > Question 2: > What is the minimum coordination between the DOS partition table > and the disk label which will allow pcfs to mount? >I can sort of guess the sequence of access while you ask the computer >to mount a pcfs is: > mbr, to find 386BSD partition > disklabel, to find the dos partition > mount it, having known the tracks/sectors/etc. >You can't mount a pcfs which resides on a disk w/o a 386 partition. >(well, I guess you can if you do some tricks in-core) > > Question 3: > Is the c partition determined by wired-in logic, or does it > depend on pc# and oc# values in disktab? This appears to be > important, since all the examples in /etc/disktab have defined > c partitions, with oc#0. >c is the 386BSD partition, and d is the whole disk. > Question 4: > Just exactly what does disklabel do? With -r, it reads from the > disk, and without, it uses an in-core copy. OK. But what's > getting edited with -e? Since -w requires a disk name, apparently > to look up in /etc/disktab, what's the point of editing? I've > apparently edited successfully by editing /etc/disktab, but not > by use of -e. >-e let you manually edit the disklabel, be it with -r or not. >-w write out disklabel according to disktab and bootfiles you provide >on the command line. > Question 5: > I have found that FDISK will place the first DOS partition of the > first disk exactly one track in from the beginning of the disk, > but it will locate the first DOS partition of the second disk one > *cylinder* in. If I use Norton's diskedit, say, to revise this to > start the second disk's DOS partition in the second track, will > DOS work? And what's the impact on the disk label? >it's just a convention. I think you can start it anywhere. >no impact on disklabel. remember, disklabel is within 386BSD >partition. > >Hope this helps. > -- > Chuck Bacon - crtb@helix.nih.gov ( alas, not my 3b1 )-: > ABHOR SECRECY - DEFEND PRIVACY How about boot manager like OS2-BM, and booteasy, when the system first starts up, what is the sequence for boot manager to identify bootable partitions from different drives ? Do they check on each of the drive's MBR and prompt the user for the one they like to boot ? How about if there are IDE's and SCSI's coexist and each has multiple bootable parition ? Thanks in advance and email replies please! - wongm@latcs1.lat.oz.au (M.C Wong) -- - wongm@latcs1.lat.oz.au