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Old 12-14-2009, 01:41 AM
jasn jasn is offline
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Join Date: Dec 2009
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Default [Solved] Dual Boot Linux/Windows 7 SSD Alignment Confusion

I have been trying to align the partitions on my SSD for a dual boot (Linux/Windows 7) configuration, and I keep running into a disk geometry corruption problem. I started with Theodore Ts'o's blog post on aligning SSDs, and I figured if I simply followed Ted's suggestions to start fdisk with the -H 224 -S 56 geometry parameters, (so I can align on 128k boundaries for my Corsair P256 SSD), and then create all of my Linux and Windows partitions, that I would be set. I don't want to use LVM. I just want to partition the drive statically for both OSes, (like I've done in the past). So I created the following partitions;

/dev/sda1 - 32M for /boot
/dev/sda2 - 35G for my Windows 7 OS
/dev/sda3 - 55G for my Windows 7 Data
/dev/sda4 - (rest of drive for extended partition)
/dev/sda5 - 4G for my Linux swap partition
/dev/sda6 - rest of drive for my Linux root partition

Creating the partitions using fdisk works fine, and if I do a fdisk -l right after I'm done, I see the geometry reported correctly as 224 heads, and 56 sectors. I even do all of my mkfs/mkntfs/mkswap steps, from the SystemRescueCD, after partitioning, and fdisk -l still reports the geometry and partitions correctly. My problem is that when I reboot to do my directed Windows 7 install to /dev/sda2, (no partitioning and no formatting), after I reboot to the SystemRescueCD again, to begin my Linux install, I find that the disk geometry has been corrupted by the Windows installation. When I look at the disk again with fdisk -l, it reports that the drive geometry is now the default 255 heads and 63 sectors, and that partitions do not end on cylinder boundaries. Like this;
root@sysresccd /root % fdisk -l

Disk /dev/sda: 256.1 GB, 256060514304 bytes
255 heads, 63 sectors/track, 31130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0xf7c8e09a

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1           4       31332   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2   *           4        4574    36703744    7  HPFS/NTFS
/dev/sda3            4574       11754    57677312    7  HPFS/NTFS
Partition 3 does not end on cylinder boundary.
/dev/sda4           11754       31131   155645952    5  Extended
Partition 4 does not end on cylinder boundary.
/dev/sda5           11754       12277     4202212   82  Linux swap / Solaris
/dev/sda6           12277       31131   151443684   83  Linux
When I look at the drive with the original fdisk geometry parameters, it shows up as;
root@sysresccd /root % fdisk -H 224 -S 56 -l   

Disk /dev/sda: 256.1 GB, 256060514304 bytes
224 heads, 56 sectors/track, 39869 cylinders
Units = cylinders of 12544 * 512 = 6422528 bytes
Disk identifier: 0xf7c8e09a

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1           5       31332   83  Linux
/dev/sda2   *           6        5857    36703744    7  HPFS/NTFS
Partition 2 does not end on cylinder boundary.
/dev/sda3            5858       15053    57677312    7  HPFS/NTFS
/dev/sda4           15054       39869   155645952    5  Extended
/dev/sda5           15054       15723     4202212   82  Linux swap / Solaris
/dev/sda6           15724       39869   151443684   83  Linux
This is happening exactly the same way on two different P256 SSDs in two different laptops. So after having manually partitioned the drive under Linux with fdisk, and then simply installed Windows 7, not only is the drive not reporting the correct geometry, it now reports that one, (or several), of the partitions do not end on cylinder boundaries. This is strangely reminiscent of the 2005 bug in Fedora Core 2 that caused the hard disk geometry as reported in the partition table to be altered during Linux installation, for dual boot (Fedora/XP) systems.

I also tried doing this from Windows. I booted the Windows 7 install disc, and then created all the same partitions as above with the Windows command line disk partition tool, diskpart.exe, (which defaults to a 1024K offset for the first partition). I then installed Windows 7, and then rebooted with the SystemRescueCD to install Linux, and fdisk -l again showed a geometry of 255 heads, 63 sectors, (which may or may not have been correct. I don't know how to check the geometry from diskpart), but also partition 1 not ending on a cylinder boundary. I've read this Microsoft Technet forum post that suggest that some Windows 7 users having problems with formatting floppy disks, because of Windows 7 corrupting the disk geometry. I don't know if this is related to that or not. Has anyone else seen anything like this?

BTW, the only way I was able to get through an SSD partition -> installation of Windows 7 -> and then an installation of Linux, without fdisk reporting corrupted disk geometries, was to start all over with fdisk, and partition the SSD with the default disk geometry parameters only, fdisk /dev/sda. In other words, run fdisk without any additional drive parameters.


Last edited by jasn; 04-22-2010 at 07:10 PM.
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