Re: Dangerously dedicated vs. fully dedicated, etc.
In <[EMAIL PROTECTED]>, Ian Dowse <[EMAIL PROTECTED]> typed: > In message <[EMAIL PROTECTED]>, [EMAIL PROTECTED] writes: > >Mike, I'll pay back your effort in replying to this long thing by > >working up a patch for the "disklabel" manpage (at least) and, if you > >want, I'll CC you so you can veto things you don't like. I do worry > (B) Dedicated format created by sysinstall > > > > sector 0: boot1 and the DOS slice table, where > the slice table contains one slice > (slice 1) covering the entire disk, > including sector 0. > sector 1: disklabel > sector 2-15:boot2 > sectors 16-31: 'a' partition filesystem superblock > > In this case, there is no boot0, and boot1 serves as the boot > loader that is invoked by the BIOS. Here, all of the boot code > is contained within the first slice and also within the first > partition. Again, the 8k reserved at the start of every ffs > filesystem protects the boot code. Sysinstall sets up fstab to > refer to the partitions as e.g. /dev/ad0s1a (I think). This can also be referred to as /dev/ad0a, like your C case. I personally prefer that because it lets you know that the disk is DD. http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information. ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Dangerously dedicated vs. fully dedicated, etc.
In <[EMAIL PROTECTED]>, Ian Dowse <[EMAIL PROTECTED]> typed: > As to the issue of BIOSes disliking DD modes, there have been a few > different reasons suggested. I had a dual xeon BIOS that had "anti-virus" code. If the boot block didn't have the write MBR on it, it rewrote the first 63 sectors, clobbering my DD (type B) disklabel. It could be turned off in the BIOS, but caused me (not the kernel) to panic the first time it happened. http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information. ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Dangerously dedicated vs. fully dedicated, etc.
Mike Meyer <[EMAIL PROTECTED]> writes: > As you can see, it's sector 1, not sector 0. Everything else seems to > be correct. More terminology problems. "1" means "0". Says "fdisk": Warning: BIOS sector numbering starts with sector 1 To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
Re: Dangerously dedicated vs. fully dedicated, etc.
In <[EMAIL PROTECTED]>, Gary W. Swearingen <[EMAIL PROTECTED]> typed: > Ian Dowse <[EMAIL PROTECTED]> writes: > You've cleared up several things, thanks. (I still don't see why any > BIOS would have trouble with a DD disk, leading to DD's deprecation, but > I can just take people's word for it, for the task at hand.) BTW, I've > seen both of your options referred to as DD, if I understood it right. There are BIOSes out there that check sector 0, and fail to recognize the disk if it if the MBR doesn't conform to their idea of "valid". Some of them will overwite sector 0 with a "valid" MBR in that case. I've had this happen to me, meaning my disk was fried every time I rebooted the system - until I turned off the "Virus protection" feature of the BIOS. > > (C) Dedicated format using dummy slice > ... > One such as would be created by "disklabel -B". (/boot/boot1 seems to > have the fourth slice pre-defined.) This differs from "B" only in the > slice table, right? The "disklabel" manpage implies that this is a DD. Yes, the slice table is the only difference. This is what you get if you install a "dangerously dedicated" disk with the i386 installer. In fact, I've got one here: Information from DOS bootblock is: The data for partition 1 is: sysid 165,(FreeBSD/NetBSD/386BSD) start 0, size 17942584 (8761 Meg), flag 80 (active) beg: cyl 0/ head 0/ sector 1; end: cyl 1023/ head 17/ sector 4 The data for partition 2 is: The data for partition 3 is: The data for partition 4 is: > It seems that a DD disk is one which is similar to a single slice > starting at sector 0, regardless of what the slice table part of sector > 0 contains. With FreeBSD-standard boot code and some BIOSes, one disk > layout (ie, DD or sliced) will work better than the other. (And for DD > disks, some slice table contents might work better than others. I've > not read anything comparing your "B" and "C" or either with a slice > table full of zeros or random bits.) As you can see, it's sector 1, not sector 0. Everything else seems to be correct. http://www.mired.org/consulting.html Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
Re: Dangerously dedicated vs. fully dedicated, etc.
In <[EMAIL PROTECTED]>, Gary W. Swearingen <[EMAIL PROTECTED]> typed: > Mike, I'll pay back your effort in replying to this long thing by > working up a patch for the "disklabel" manpage (at least) and, if you > want, I'll CC you so you can veto things you don't like. I do worry > about how so few people comment on manpage changes before they go in, > but they need improvement so badly it's worth the risk of a few errors. > If you can't reply or even read it, that's OK too; I think I learned > something in the writing of it. I'd be more than happy to review any changes you make. And I'm happy to see you turning things into something more substantial than an archived message. http://www.mired.org/consulting.html Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
Re: Dangerously dedicated vs. fully dedicated, etc.
In message <[EMAIL PROTECTED]>, [EMAIL PROTECTED] writes: >/boot/boot0 has the FreeBSD bootloader. The installer also offers >to use the "standard" /boot/mbr. >Roughly speaking. /boot/boot2 is 15 sectors; I suppose the first >(all zeros) is replaced with the disklabel, loosely speaking. >One such as would be created by "disklabel -B". (/boot/boot1 seems to >have the fourth slice pre-defined.) This differs from "B" only in the >slice table, right? The "disklabel" manpage implies that this is a DD. Exactly. Thanks for filling in the details I missed. The other magic thing about the bogus 5-sector slice is that the kernel detects this special case and then completely ignores the slice table and makes the compatibility slice cover the whole disk (I'm not 100% sure of the details here). >It seems that a DD disk is one which is similar to a single slice >starting at sector 0, regardless of what the slice table part of sector >0 contains. With FreeBSD-standard boot code and some BIOSes, one disk >layout (ie, DD or sliced) will work better than the other. (And for DD >disks, some slice table contents might work better than others. I've >not read anything comparing your "B" and "C" or either with a slice >table full of zeros or random bits.) I think to avoid warnings or errors, you need either a valid slice entry (even if it is a sysinstall-style slice that starts at sector 0 and contains the whole disk), or else the exact special bogus slice table, since the kernel code just does a bcmp() to check for the special bogus table. As to the issue of BIOSes disliking DD modes, there have been a few different reasons suggested. For traditional BIOSes that just look for the 0x55 0xaa signature and if found then execute the MBR code, all of the various DD and non-DD schemes should work fine. However, some BIOSes perform additional tests that may fail on DD disks. For example (I'm just guessing here), they might check that the slice starts after the MBR, or that the slice starts and ends on a cylinder boundary. It sounds a silly thing to do, but I guess maybe it allows the BIOS to automatically figure out what geometry the OS is expecting or something. The fact that boot1 always contains the bogus slice table even when boot1 is not used as an MBR has been linked to other BIOS problems too - some BIOSes apparently go further and check if the first sector of each slice looks like it has an extended partition table even if the slice type is not that of an extended partition. In -CURRENT, the default bogus slice table was changed slightly to stop some BIOSes crashing with a divide-by-zero error when they tried to parse the bogus slice entry in boot1. Ian To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
Re: Dangerously dedicated vs. fully dedicated, etc.
Ian Dowse <[EMAIL PROTECTED]> writes: > At the risk of adding to the confusion, here is a less wordy > description of the various disk layouts. The term `dangerously > dedicated' seems to be used to refer to either options (B) or (C), > so I will avoid using that term: You've cleared up several things, thanks. (I still don't see why any BIOS would have trouble with a DD disk, leading to DD's deprecation, but I can just take people's word for it, for the task at hand.) BTW, I've seen both of your options referred to as DD, if I understood it right. > (A) Normal sliced disk (assuming sectors/track = 63) > > sector 0: boot0 and the DOS slice table /boot/boot0 has the FreeBSD bootloader. The installer also offers to use the "standard" /boot/mbr. > > (B) Dedicated format created by sysinstall ... > sector 1: disklabel > sector 2-15:boot2 Roughly speaking. /boot/boot2 is 15 sectors; I suppose the first (all zeros) is replaced with the disklabel, loosely speaking. The installer (and its code) calls this a DD disk. > (C) Dedicated format using dummy slice ... One such as would be created by "disklabel -B". (/boot/boot1 seems to have the fourth slice pre-defined.) This differs from "B" only in the slice table, right? The "disklabel" manpage implies that this is a DD. It seems that a DD disk is one which is similar to a single slice starting at sector 0, regardless of what the slice table part of sector 0 contains. With FreeBSD-standard boot code and some BIOSes, one disk layout (ie, DD or sliced) will work better than the other. (And for DD disks, some slice table contents might work better than others. I've not read anything comparing your "B" and "C" or either with a slice table full of zeros or random bits.) Thanks again. To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
Re: Dangerously dedicated vs. fully dedicated, etc.
In message <[EMAIL PROTECTED]>, [EMAIL PROTECTED] writes: >Mike, I'll pay back your effort in replying to this long thing by >working up a patch for the "disklabel" manpage (at least) and, if you >want, I'll CC you so you can veto things you don't like. I do worry At the risk of adding to the confusion, here is a less wordy description of the various disk layouts. The term `dangerously dedicated' seems to be used to refer to either options (B) or (C), so I will avoid using that term: (A) Normal sliced disk (assuming sectors/track = 63) sector 0: boot0 and the DOS slice table sectors 1..62:unused sector 63:boot1 sector 64:disklabel sectors 65-78:boot2 sectors 79-92:'a' partition filesystem superblock Note that the disklabel, which contains a list of the partitions within a slice is actually contained within the space allocated to the first partition. To ensure that this does not get clobbered by the filesystem, the first 8k of every ffs filesystem is reserved for boot code and the disklabel. (B) Dedicated format created by sysinstall sector 0: boot1 and the DOS slice table, where the slice table contains one slice (slice 1) covering the entire disk, including sector 0. sector 1: disklabel sector 2-15: boot2 sectors 16-31:'a' partition filesystem superblock In this case, there is no boot0, and boot1 serves as the boot loader that is invoked by the BIOS. Here, all of the boot code is contained within the first slice and also within the first partition. Again, the 8k reserved at the start of every ffs filesystem protects the boot code. Sysinstall sets up fstab to refer to the partitions as e.g. /dev/ad0s1a (I think). (C) Dedicated format using dummy slice sector 0: boot1 and the DOS slice table. The slice table contains a single entry (slice 4) that starts at sector 0 and has a size of 5 sectors, whatever the real disk size is. sector 1: disklabel sector 2-15: boot2 sectors 16-31:'a' partition filesystem superblock This is like (B) except that slice 4 instead of slice 1 is used, and the size of the slice in the slice table is bogus. The partitions on such a disk are usually accessed using the compatibility slice names such as /dev/ad0a. Ian To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
Re: Dangerously dedicated vs. fully dedicated, etc.
Mike, I'll pay back your effort in replying to this long thing by working up a patch for the "disklabel" manpage (at least) and, if you want, I'll CC you so you can veto things you don't like. I do worry about how so few people comment on manpage changes before they go in, but they need improvement so badly it's worth the risk of a few errors. If you can't reply or even read it, that's OK too; I think I learned something in the writing of it. Mike Meyer <[EMAIL PROTECTED]> writes: > In <[EMAIL PROTECTED]>, Gary W. Swearingen <[EMAIL PROTECTED]> >typed: > > I'm having trouble understanding a couple parts of the "disklabel" > > manpage related to dangerously/fully dedicated disks. > > > > The "BUGS" section has this paragraph: > > > > For the i386 architecture, the primary bootstrap sector contains an > > embedded fdisk table. The disklabel utility takes care to not > > clobber it when installing a bootstrap only (-B), or when editing an > > existing label (-e), but it unconditionally writes the primary > > bootstrap program onto the disk for -w or -R, thus replacing the > > fdisk table by the dummy one in the bootstrap program. This is only > > of concern if the disk is fully dedicated, so that the BSD disklabel > > starts at absolute block 0 on the disk. > > > > 1) Can anyone explain that last sentence to me? Shouldn't that "is only > > of concern" instead be "is not of concern", reversing the sense? > > No, it's right. But you say that a fully dedicated disk has a standard disklabel. So the fdisk table is the dummy one, by definition of "standard". So why would replacing it with another dummy one concern me (as the quote says it should)? I now suspect that "fully" means "dedicated", and I should be concerned that it's fake fdisk table not get overwritten (but I don't see why it even needs a fake table -- more below). And if I have normally sliced disk, whouldn't I also be concerned if "disklabel" was going to "replace the fdisk table" when it "writes the primary bootstrap program"? That depends on definitions. I was confused by FreeBSD referring to boot1 as the "primary bootstrap" while it seems so obvious that boot0 (MBR) is the primary bootstrap. The about manpage quote seemed to imply that the MBR's "fdisk table" could be overwritten; made even more wrong because there is no other fdisk table, really. The boot1 dummy table is not an "fdisk table" because fdisk knows nothing about it on a sliced disk. I think "only of concern if" should be "only true if". I think there's a terminology mess here. Looking further, I see that my filesystem has a block size of 16384, but disklabel.c seems to use a "boot block" size of 8192 (presumably to fit in /boot/boot1 (512) and /boot/boot2 (7680, part of which is a placeholder for the disklabel sector); which the code refers to as "block 0" and "block 1-15"! > > 2) Is a "fully dedicated" disk exactly the same as a "dangerously > > dedicated" disk? If not, what's the difference? Can one use a disk > > (or a slice) which has no space reserved for stage 1 & 2 boot records, > > say, for a non-bootable disk? I know no way to disklabel one that way. > > I've never seen "fully dedicated" anywhere else, so I can't say for > sure. However, I suspect they are using that to distinguish a drive on > a non-PC system - which has a standard disklabel in block 0 - from a > dangerously dedicated drive, which has a dangerously dedicated > disklabel in block 0. So then what's the difference between "a standard disklabel" and "a dangerously dedicated disklabel"? Is it only that the std one has a dummy partition table and the DD one has a "fake" table, where "dummy" means "whatever is in boot1 (some warning text?)" and "fake" means "some data as if the disk was sliced"? (More below.) > > 3) Is "block 0" exactly the same as "sector 0"? > > No. Block 0 is a file system block, whose size depends on the > parameters you gave newfs when you created the file system. I've seen > reports that booting won't work if you don't use the default values on > the root file system, but have never verified them. Sector 0 is the > first sector of block 0. It looked to me like disklabel.c is using 8192, regardless of FS params. I don't know why my root FS has 16384 since it's less than 1 GB so it's supposed to be 8192. But it boots. > > 4) Shouldn't "BSD disklabel starts at absolute block 0" be "FreeBSD > > stage 1 boot record starts at sector 0"? The disklabel immediately > > follows the stage 1 boot record, right? So it would be "block 1"? > > No, both the stage 1 boot and the disklabel are in block 0. OK, I guess the "block 0" is true (but confusing), but I like your disklabel "in block 0" a lot better than the manpages's "starts at block 0". > > Under "Writing a standard label", the manpage says: > > > > PC-based systems have special requirements in order for the BIOS to > > properly recognize a FreeBSD disklabel. Older sys
Re: Dangerously dedicated vs. fully dedicated, etc.
In <[EMAIL PROTECTED]>, Gary W. Swearingen <[EMAIL PROTECTED]> typed: > I'm having trouble understanding a couple parts of the "disklabel" > manpage related to dangerously/fully dedicated disks. > > The "BUGS" section has this paragraph: > > For the i386 architecture, the primary bootstrap sector contains an > embedded fdisk table. The disklabel utility takes care to not > clobber it when installing a bootstrap only (-B), or when editing an > existing label (-e), but it unconditionally writes the primary > bootstrap program onto the disk for -w or -R, thus replacing the > fdisk table by the dummy one in the bootstrap program. This is only > of concern if the disk is fully dedicated, so that the BSD disklabel > starts at absolute block 0 on the disk. > > 1) Can anyone explain that last sentence to me? Shouldn't that "is only > of concern" instead be "is not of concern", reversing the sense? No, it's right. > 2) Is a "fully dedicated" disk exactly the same as a "dangerously > dedicated" disk? If not, what's the difference? Can one use a disk > (or a slice) which has no space reserved for stage 1 & 2 boot records, > say, for a non-bootable disk? I know no way to disklabel one that way. I've never seen "fully dedicated" anywhere else, so I can't say for sure. However, I suspect they are using that to distinguish a drive on a non-PC system - which has a standard disklabel in block 0 - from a dangerously dedicated drive, which has a dangerously dedicated disklabel in block 0. > 3) Is "block 0" exactly the same as "sector 0"? No. Block 0 is a file system block, whose size depends on the parameters you gave newfs when you created the file system. I've seen reports that booting won't work if you don't use the default values on the root file system, but have never verified them. Sector 0 is the first sector of block 0. > 4) Shouldn't "BSD disklabel starts at absolute block 0" be "FreeBSD > stage 1 boot record starts at sector 0"? The disklabel immediately > follows the stage 1 boot record, right? So it would be "block 1"? No, both the stage 1 boot and the disklabel are in block 0. > Under "Writing a standard label", the manpage says: > > PC-based systems have special requirements in order for the BIOS to > properly recognize a FreeBSD disklabel. Older systems may require > what is known as a ''dangerously dedicated'' disklabel, which > creates a fake DOS partition to work around problems older BIOSes > have with modern disk geometries. > > 5) What's "fake DOS partition"? DD disks don't have partitions. Is it > just trying to not bother saying that it fills in the MBR partition > table as if there was at least one slice which the DD MBR will ignore. DD disks don't have fdisk partitions, but they have an fdisk table. It has one partition that covers the entire disk. That's probably what they are referring to. Note that the system also supports accessing the drive as if it had one fdisk partition, so that da0s1a and da0a reference the same bit of disk if da0 is DD. > 6) Why is the problem limited to older systems? Don't new BIOSes > check for a normal-looking partition table? The BIOS checking the fdisk table isn't what you're avoiding with a DD disk. What you're avoiding is the BIOS geometry calculations at boot time. Older BIOSes apparently have trouble with that. > 7) Isn't the first sentence wrong? BIOS don't look for disklabels, do > they? The special requirements are in order for the BIOS to find the > FreeBSD stage 1 boot record, no?. (And the FreeBSD installer doesn't > satisfy the requirements for non-DD disks (as I read the FAQ's DD > answer). I can't imagine why not. Older systems with a standard > MBR boot any active slice (even FreeBSD) without problems, no?) I think the first sentence has confusing wording, in that PC BIOSes could be confused if there wasn't an fdisk table. It should say "recognize disks with a FreeBSD disklabel." A standard FreeBSD disklabel does *not* have an fdisk table in it. That's what gets put at the beginning of fdisk partitions, and at the beginning of disks on non-PC based systems. If you put that at the beginning of a disk on a PC, you could confuse the BIOS. The special requirements are that you have an fdisk table. On non-DD disks, the FreeBSD installer installs either a standard MBR or a boot0 MBR, both of which have an fdisk table. It then installs standard disk labels on the fdisk partitions, where they won't confuse anything. http://www.mired.org/consulting.html Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
Dangerously dedicated vs. fully dedicated, etc.
I'm having trouble understanding a couple parts of the "disklabel" manpage related to dangerously/fully dedicated disks. The "BUGS" section has this paragraph: For the i386 architecture, the primary bootstrap sector contains an embedded fdisk table. The disklabel utility takes care to not clobber it when installing a bootstrap only (-B), or when editing an existing label (-e), but it unconditionally writes the primary bootstrap program onto the disk for -w or -R, thus replacing the fdisk table by the dummy one in the bootstrap program. This is only of concern if the disk is fully dedicated, so that the BSD disklabel starts at absolute block 0 on the disk. 1) Can anyone explain that last sentence to me? Shouldn't that "is only of concern" instead be "is not of concern", reversing the sense? 2) Is a "fully dedicated" disk exactly the same as a "dangerously dedicated" disk? If not, what's the difference? Can one use a disk (or a slice) which has no space reserved for stage 1 & 2 boot records, say, for a non-bootable disk? I know no way to disklabel one that way. 3) Is "block 0" exactly the same as "sector 0"? 4) Shouldn't "BSD disklabel starts at absolute block 0" be "FreeBSD stage 1 boot record starts at sector 0"? The disklabel immediately follows the stage 1 boot record, right? So it would be "block 1"? Under "Writing a standard label", the manpage says: PC-based systems have special requirements in order for the BIOS to properly recognize a FreeBSD disklabel. Older systems may require what is known as a ''dangerously dedicated'' disklabel, which creates a fake DOS partition to work around problems older BIOSes have with modern disk geometries. 5) What's "fake DOS partition"? DD disks don't have partitions. Is it just trying to not bother saying that it fills in the MBR partition table as if there was at least one slice which the DD MBR will ignore. 6) Why is the problem limited to older systems? Don't new BIOSes check for a normal-looking partition table? 7) Isn't the first sentence wrong? BIOS don't look for disklabels, do they? The special requirements are in order for the BIOS to find the FreeBSD stage 1 boot record, no?. (And the FreeBSD installer doesn't satisfy the requirements for non-DD disks (as I read the FAQ's DD answer). I can't imagine why not. Older systems with a standard MBR boot any active slice (even FreeBSD) without problems, no?) To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
