[CentOS] Analyzing the MBR

Thu Jun 5 20:56:05 UTC 2014
m.roth at 5-cent.us <m.roth at 5-cent.us>

John R Pierce wrote:
> On 6/5/2014 12:07 PM, Timothy Murphy wrote:
>> That doesn't really answer my question;
>> I know (roughly) what the MBR, ie the first 512 bytes, contains.
>> But I notice that my laptop, for example, leaves 64 sectors
>> for something at the start of the disk;
>> and when I get the first 2048 bytes with
>>    sudo dd if=/dev/sda of=sda.mbr bs=2048 count=1
>> I see that there is plenty on the disk after the first 512 bytes.
>> (Admittedly Windows might have written that, as I have a Windows
>> partition.)
>> But does Linux ever write anything in bytest 513-1024, for example?
> traditional PC partitioning tools, dating back to MSDOS, put partitions
> on 'cylinder' boundaries.   this is a bad idea on modern disks, whether
> they be SSD's that often have 128K physical write blocks, or newer HD's
> with 4096 byte physical sectors, or raids where there's several of the
> above striped together.
> the rest of the space between the sector 0 MBR and the first primary
> partition is completely empty, nothing puts anything there.
> I always start my first partition at a round number SECTOR, like 128s
> (which is 64k bytes assuming 512B sectors) so everything is aligned on a
> power-of-two boundary....   I use parted, rather than fdisk, to do
> this.   something like...
> parted -a min /dev/sdb
> mklabel gpt
> mkpart pri 128s -1s
> quit
I find
mkpart pri 0.0GB x.GB
*always* gives me aligned partions (and parted - talk about user hostile
programs! "Not aligned", with not a clue as to what it actually wants....)