Re: [gentoo-user] Re: Who believes in cylinders?

[David W Noon]

On Sun, 28 Feb 2010 13:10:02 +0100, Mick wrote about Re: [gentoo-user]
Re: Who believes in cylinders?:

>On Saturday 27 February 2010 18:20:24 Etaoin Shrdlu wrote:
>> On Saturday 27 February 2010, BRM wrote:
>> >  Stage 1 focuses solely on loading Stage 2,
>> >  and has historically been limited to a total size[1] to 512 bytes,
>>
>> It's actually less than that, because the first 64 bytes of sector 0
>>  contain the partition table, so the maximum size of a stage1
>> bootloader is 510 - 64 = 446 bytes.
>
>Yep, that's why dd if=/dev/sda of=~/partition_table.img bs=446 count=1
>will make you a nice back up of your partition table,

Actually, it will backup your primary bootstrap code.  Try:

dd if=/dev/sda of=~/partition_table.img bs=1 skip=446 count=64

Note that you will need to be root or in the "disk" group (or
equivalent on your system), so that you have access to /dev/sda as a
raw device file. [As ever, sudo is your friend.]

Also note that this backup will only contain the primary partitions and
any extended partition on that disk; all the logical drives within the
extended partition are mapped by secondary partition tables in their
local bootstrap records (LBRs).  This makes for a more complicated
process to backup the complete partition table for the disk.

Worse still, all of my machines have at least 4 hard drives -- some as
many as 7. So this process has to be repeated for each physical disk.

Many years ago I wrote an OS/2 program to handle all of this. Perhaps I
should blow the dust off it, convert it to use POSIX functions and
publish it as FOSS.

> while bs=512 will back up your complete MBR.

True.
-- 
Regards,

Dave  [RLU #314465]
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dwnoon@××××××××.com (David W Noon)
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