[CentOS] Analyzing the MBR

Thu Jun 5 21:50:31 UTC 2014
Les Mikesell <lesmikesell at gmail.com>

On Thu, Jun 5, 2014 at 4:00 PM, John R Pierce <pierce at hogranch.com> wrote:
> On 6/5/2014 1:56 PM, m.roth at 5-cent.us wrote:
>> 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....)
> I've taken to always running parted with -a none, as its alignment rules
> are based on old concepts like cylinders, heads, which are meaningless
> and even WRONG on today's storage devices. (63 heads, 255 sectors is not
> uncommon, this means everything at a cylinder or head is on an ODD
> sector boundary, ouch!)

New bigger disks may use 4k physical sectors but report 512 for
backwards compatibility.  If you don't write 4 contiguous sectors it
has to read, wait for the disk to spin back around, then write,
merging in what you did write.  Which means writes will be very slow
if your partitions are not aligned on 4k boundaries. I haven't had to
deal with many of these yet so I've mostly just installed gparted from
epel and used its defaults rather than doing the math myself.

  Les Mikesell
    lesmikesell at gmail.com