Fussing around with setting up a Linux/Win2k dual boot system, I have
taken to making backups of the MBR, and even seperate backups of the
partition table.

Making myself more familiar with the latter, I realised that bytes
447-510 in the MBR contain only the information of the *primary* four
partitions, which isn't so surprising after all, given it holds
exactly four entries.

If you have an extended partition, thus, it follows there must be an
extra partition table for this partition. I seem to have read
somewhere that the extended partition contains a similar ("master" or
not) boot record which is also equivalent to the first 512 bytes. But,
since an extended partition may hold more than 4 logical partitions,
its partition table cannot be at the same offset as the partition
table is in the MBR of the whole disk.

Can someone tell me where it is exactly located? The reason I want to
backup it ("back it up"?) is I don't trust W2k at all, and there is
already a full Linux installation on a logical partition which I'd
like to keep.

Many thanks for enlightenment


Florian v. Savigny

If you are going to reply in private, please be patient, as I only
check for mail something like once a week. - Si vous allez répondre
personellement, patientez s.v.p., car je ne lis les courriels
qu'environ une fois par semaine.

[ Post a follow-up to this message ]

"Florian von Savigny" <florian265@uboot.com> wrote in message
news:m3brir53bj.fsf@uboot.com...
>
> Fussing around with setting up a Linux/Win2k dual boot system, I have
> taken to making backups of the MBR, and even seperate backups of the
> partition table.
>
> Making myself more familiar with the latter, I realised that bytes
> 447-510 in the MBR contain only the information of the *primary* four
> partitions, which isn't so surprising after all, given it holds
> exactly four entries.
>
> If you have an extended partition, thus, it follows there must be an
> extra partition table for this partition. I seem to have read
> somewhere that the extended partition contains a similar ("master" or
> not) boot record which is also equivalent to the first 512 bytes. But,
> since an extended partition may hold more than 4 logical partitions,
> its partition table cannot be at the same offset as the partition
> table is in the MBR of the whole disk.
>
> Can someone tell me where it is exactly located? The reason I want to
> backup it ("back it up"?) is I don't trust W2k at all, and there is
> already a full Linux installation on a logical partition which I'd
> like to keep.
>
> Many thanks for enlightenment
>
>
> Florian v. Savigny
>
> If you are going to reply in private, please be patient, as I only
> check for mail something like once a week. - Si vous allez répondre
> personellement, patientez s.v.p., car je ne lis les courriels
> qu'environ une fois par semaine.

Maybe try using `sfdisk` under linux. It has an option to dump the partition
table to a file that is useful
as input to sfdisk.

- To save
# sfdisk -d /dev/hda > /tmp/hda.save

- To restore:
# sfdisk < /tmp/hda.save

This is all in the man page for sfdisk
# man sfdisk

Nick

[ Post a follow-up to this message ]

Florian von Savigny <florian265@uboot.com> wrote:
>
> Fussing around with setting up a Linux/Win2k dual boot system, I have
> taken to making backups of the MBR, and even seperate backups of the
> partition table.
>
> Making myself more familiar with the latter, I realised that bytes
> 447-510 in the MBR contain only the information of the *primary* four
> partitions, which isn't so surprising after all, given it holds
> exactly four entries.
>
> If you have an extended partition, thus, it follows there must be an
> extra partition table for this partition. I seem to have read
> somewhere that the extended partition contains a similar ("master" or
> not) boot record which is also equivalent to the first 512 bytes. But,
> since an extended partition may hold more than 4 logical partitions,
> its partition table cannot be at the same offset as the partition
> table is in the MBR of the whole disk.
>
> Can someone tell me where it is exactly located? The reason I want to
> backup it ("back it up"?) is I don't trust W2k at all, and there is
> already a full Linux installation on a logical partition which I'd
> like to keep.
>
> Many thanks for enlightenment
>
>
> Florian v. Savigny
>
> If you are going to reply in private, please be patient, as I only
> check for mail something like once a week. - Si vous allez r?pondre
> personellement, patientez s.v.p., car je ne lis les courriels
> qu'environ une fois par semaine.

Get the doc files for lilo, they go into exhaustive detail on extended
partitions.

Jerry

[ Post a follow-up to this message ]

Thanks to both of you for hinting at information sources. Maybe I'll
take to reading the lilo documentation later

I have tried out sfdisk, which does indeed even make binary copies of
the whole partition table. However, these binary copies seem to be
useful only if you have sfdisk available to restore them to the right
places, which might not be the case in the case of an
emergency. Moreover, sfdisk makes these backups only immediately
before it *changes* the partition table. Thus, to make a backup, you
have to specify an action that writes to the partition table, but
without actually changing anything (such as making the first partition
bootable when it is bootable anyway). I don't feel exactly safe with
such an approach.

Hence, I have resorted to making a human-readable backup, such as
sfdisk makes with the option -d (which sfdisk can also use to
automatically restore the partition table, so it's as good as the
binary backup in that respect).

I begin to understand now why people simply make printouts of the
partition table ... BTW, there's one treacherous detail that has
turned up: partition boundaries seem to be exact only if they are
specified in sectors, so that's how one should make human-readable
forms of backup (and it renders my recent recovery of my Linux
partition unsafe: I'll reinstall the whole thing).


--


Florian v. Savigny

If you are going to reply in private, please be patient, as I only
check for mail something like once a week. - Si vous allez répondre
personellement, patientez s.v.p., car je ne lis les courriels
qu'environ une fois par semaine.

[ Post a follow-up to this message ]

"Florian von Savigny" <florian265@uboot.com> wrote in message
news:m3brir53bj.fsf@uboot.com...
>
> Fussing around with setting up a Linux/Win2k dual boot system, I have
> taken to making backups of the MBR, and even seperate backups of the
> partition table.
>
> Making myself more familiar with the latter, I realised that bytes
> 447-510 in the MBR contain only the information of the *primary* four
> partitions, which isn't so surprising after all, given it holds
> exactly four entries.
>
> If you have an extended partition, thus, it follows there must be an
> extra partition table for this partition. I seem to have read
> somewhere that the extended partition contains a similar ("master" or
> not) boot record which is also equivalent to the first 512 bytes. But,
> since an extended partition may hold more than 4 logical partitions,
> its partition table cannot be at the same offset as the partition
> table is in the MBR of the whole disk.
>
> Can someone tell me where it is exactly located? The reason I want to
> backup it ("back it up"?) is I don't trust W2k at all, and there is
> already a full Linux installation on a logical partition which I'd
> like to keep.
>
> Many thanks for enlightenment
>
>
> Florian v. Savigny
>
> If you are going to reply in private, please be patient, as I only
> check for mail something like once a week. - Si vous allez répondre
> personellement, patientez s.v.p., car je ne lis les courriels
> qu'environ une fois par semaine.


Maybe try using `sfdisk` under linux. It has an option to dump the partition
table to a file that is useful
as input to sfdisk.

- To save
# sfdisk -d /dev/hda > /tmp/hda.save

- To restore:
# sfdisk < /tmp/hda.save

This is all in the man page for sfdisk
# man sfdisk

Nick

[ Post a follow-up to this message ]

Not so much for the purposes of backing it up, but if you
also want to understand the structure a bit more, try also adding
the -x option to sfdisk.  That'll help one see much more of how the
extended partition stuff works.

"SFD" <sfd@adelphia.net> wrote in message news:<I62dnW7IDpfT43DdRVn-sA@adelphia.com>...[vbco
l=seagreen]
> "Florian von Savigny" <florian265@uboot.com> wrote in message
> news:m3brir53bj.fsf@uboot.com... 
>
>
> Maybe try using `sfdisk` under linux. It has an option to dump the partiti
on
> table to a file that is useful
> as input to sfdisk.
>
>  - To save
>   # sfdisk -d /dev/hda > /tmp/hda.save
>
>  - To restore:
>   # sfdisk < /tmp/hda.save
>
> This is all in the man page for sfdisk
>   # man sfdisk
>
> Nick[/vbcol]

[ Post a follow-up to this message ]