Hi, List;

As we know that, when a disk is *normal*, it's easy to backup its partition tables by sfdisk:

/sbin/sfdisk -d /dev/sdX > sdX.partion-table

when the partition is larger than 2TB, sfdisk cannot work properly, so how can I backup the partition table this time?
Is there anyone tried this?

Thanks & regards
joseph

The partition table is only 64 bytes....if fdisk or sfdisk can't read the partition table for large partitions, you can always copy the partition table using dd. The will not get all the extended/logical partitions, however.

Main partition table (for the first hard disk):
dd if=/dev/sda of=PT.bak bs=1 skip=446 count=64

Extended and logical (if extended is sda4):
dd if=/dev/sda4 of=PT_ext.bak bs=1 skip=446 count=64
dd if=/dev/sda5 of=PT_L1.bak bs=1 skip=446 count=64
dd if=/dev/sda6 of=PT_L2.bak bs=1 skip=446 count=64
.
.
repeat as required.
This gives you the linked list for all the logical partitions

Hmmmmmm---someone must have written a script to automate this??

The partition table in each of the EBRs (Extended Boot Records) is not found at the beginning of the logical partition, so the commands above will not quite work. The EBRs are generally located 63 sectors before the start of the logical partitions, but that is not a hard rule, and there are many exceptions depending on how the extended partition is set up (including whether the logical partitions are in physical order or not). The bottom line is a MS-DOS partition table uses a 4 byte LBA word for the sector position of the partitions, so that means you are limited to a drive size of 2 TB:
So if the drive is larger than 2 TB, one should not be using a standard MS-DOS partition table to begin with; you would have to use GPT or some other format that supports larger drives.

OOOOOOOPS!!!!

I was in a hurry, and I could swear it worked when I tried it.

do fdisk /dev/sda, and then enter the "u" option to display by sector. Use those sector numbers with the dd command----You'll see a 63-sector gap in front of every logical partition. The "EBR" is in the sector after the end of each logical.

Me be more careful next time......