Bug#614632: Disk partitions not created along cylinder boundaries
On Tue, Feb 22, 2011 at 07:51:28PM +0100, Jaap Winius wrote:
> When a disk is partitioned, the partitions are later found to not
> end/start on cylinder boundaries. For example:
This is entirely intentional. No remotely modern disk requires
partitions to be aligned on cylinder boundaries, and cylinder alignment
is very bad indeed for performance on many modern disks (especially
SSDs, but also others). It is a relic of the old days. I would be
extremely surprised if anyone is still running Debian on a disk old
enough for this to matter.
The only reason you might still need cylinder alignment is if you have a
buggy BIOS that gets confused by non-cylinder-aligned partitions, or
sometimes if you're trying to dual-boot with an old version of Windows.
In this case, you can pass partman/alignment=cylinder as a boot
parameter to the installer. You should not do this unless you have
problems that go beyond error messages from fdisk.
> The above example was actually the result of an earlier amd64
> version of the Debian squeeze netinstaller, downloaded on the 6th of
> November 2010. (The i386 version mentioned at the beginning of this
> report was found to have this same problem yesterday and also
> involved the partitioning a set of 1 TB disks that were configured
> in a RAID1 array. Until then I had not noticed that anything was
> amiss with my earlier installations.)
>
> However, an i386 version downloaded on the 19th of June 2010 does
> not have this problem and I was able to properly complete the
> installation yesterday by starting the installation and partitioning
> the disks with this older version, but then aborting that and
> completing the procedure with the most recent version.
You have not described why cylinder alignment was bad for you, aside
from the bogus error message from fdisk (use the -c option to turn this
off). Did anything actually go wrong? Perhaps you were just confused
by fdisk being stuck in the past?
> My work method also involved using all space available on the RAID1
> volume in question for LVM2. However, after doing this I saw that
> something 56.2 bytes of disk space were marked as "unusable." This
> was the case with the disk systems that did not eventually turn out
> to end on cylinder boundaries. When it did work properly the other
> day, the left over unusable space was exactly 512 bytes.
"Something 56.2 bytes"? That doesn't make sense ...
Yes, there may be a little more unusable space now, but it should be no
more than a megabyte - in other words, a negligibly tiny fraction of the
size of the disk.
Regards,
--
Colin Watson [cjwatson@debian.org]
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