Date: Thu, 27 Apr 1995 20:15:29 -0400 From: Gene Stark <gene@starkhome.cs.sunysb.edu> To: current@FreeBSD.org Subject: Disk slicing problems Message-ID: <199504280015.UAA16200@starkhome.cs.sunysb.edu>
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Over the past week or two, I have been trying to get various systems here bootstrapped over to the new disk slicing code. I have to say, I haven't fully understood it yet, and there are some serious problems I have come up against. Perhaps somebody (Bruce?) can tell me what I am missing: (1) Though I can mount, say /dev/wd0s4e, /dev/wd0s4f on /usr and /local, I am not yet able to use /dev/wd0s4a as / and /dev/wd0s4b as swap. Is this supported? Do I have to do something special in the kernel config, like change "root on wd0" to "root on wd0s4"? (2) After having gotten a kernel booted with disk slicing turned on, I find that I am unable to modify the MBR, and I am also unable to perform certain modifications to the disklabel. My understanding was that I am supposed to be able to use /dev/rwd0 as "the whole disk", and thus access and modify the MBR that way. However, when I try, say, "fdisk -u /dev/rwd0" it fails to write the MBR, complaining that the operation is not supported. Also, whereas under older kernels I was able to perform various kinds of "dangerous" modifications to the disklabel while the system is up, I can no longer do this. For example, I had my BSD slice starting at offset 1, with the a partition starting at offset 1008. I wanted to shrink the BSD slice so that it starts at offset 1008 to coincide with the start of the a partition, but there seems to be no way to do this once the initial slice table and disklabel have been written. Any attempt to change the disklabel in this way results in a complaint that the "change would shrink an open partition". This even happened while booted from the SCSI drive and attempting to modify the wd disklabel. I had to revert to an old kernel with no disk slicing, change the MBR and disklabel, then reboot the new kernel. In summary, I would like to be able to make these "dangerous" modifications, as long as I am willing to accept whatever consequences accrue from making them on the fly. Typically, what I would want to do is rewrite the MBR and disklabel, then reboot immediately if I moved the root area or something. The current system of interlocks seems to effectively prevent me from doing anything except reloading my entire disk from scratch. (3) I do not understand what the current wisdom is as far as laying out BSD partitions with respect to cylinder boundaries. With the advent of disk slicing, the disklabel now seems to be "relativized" to the beginning of the slice, with the effect that it gets very confused about what starts at a cylinder boundary and what does not. I am not particularly thrilled about this relativization; I would prefer it if the display were made the old way, but if you weren't supposed to enter values outside the slice the disk drivers simply prevented you from changing the disklabel to that. - Gene
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