On Thu, Nov 12, 2009 at 6:18 PM, Geert Janssens <[email protected]> wrote:
> On Thursday 12 November 2009, you wrote: > > > dd if=/dev/virtualmachines/windows7-x64 of=mbr.w7-x64 bs=512 count=1 > > > > I think if you do this, you are only backing up the first 512 bytes of > the > > logical volume, not the MBR. > > > > Someone correct me if I am wrong. > > I did some tests just to be sure. As far as I can tell, dd interacts with > lvm > in exactly the same way as with a physical disk or a loop device. > > In the test I copied the first sector directly from the lvm partition or > via > the loop device. It results in exactly the same sector being copied. > > Also, if you try fdisk -l on the lvm disk or the loop device, it results in > the same output. > > Below is the output from my tests: > > [r...@aragorn:~]# losetup /dev/loop1 /dev/base/kobaltwit_f11_disk > > [r...@aragorn:~]# fdisk -l /dev/base/kobaltwit_f11_disk > > Disk /dev/base/kobaltwit_f11_disk: 10.7 GB, 10737418240 bytes > 255 heads, 63 sectors/track, 1305 cylinders > Units = cylinders of 16065 * 512 = 8225280 bytes > > Device Boot Start End Blocks Id > System > /dev/base/kobaltwit_f11_disk1 * 1 1305 10482381 83 > Linux > [r...@aragorn:~]# fdisk -l /dev/base/kobaltwit_f11_disk > > Disk /dev/base/kobaltwit_f11_disk: 10.7 GB, 10737418240 bytes > 255 heads, 63 sectors/track, 1305 cylinders > Units = cylinders of 16065 * 512 = 8225280 bytes > > Device Boot Start End Blocks Id > System > /dev/base/kobaltwit_f11_disk1 * 1 1305 10482381 83 > Linux > > [r...@aragorn:~]# dd if=/dev/base/kobaltwit_f11_disk of=mbr.lvm bs=512 > count=1 > 1+0 records in > 1+0 records out > 512 bytes (512 B) copied, 7.6e-05 seconds, 6.7 MB/s > > [r...@aragorn:~]# dd if=/dev/loop1 of=mbr.loop bs=512 count=1 > 1+0 records in > 1+0 records out > 512 bytes (512 B) copied, 0.000151 seconds, 3.4 MB/s > > [r...@aragorn:~]# diff mbr.l* > [r...@aragorn:~]# > > These test seem to indicate to me that the lvm layer in completely > transparent > to userland tools such as fdisk or dd. > > So I still think the losetup step is superfluous and possibly causing > unnecessary overhead. > > Geert > > -- > Kobalt W.I.T. > Web & Information Technology > Brusselsesteenweg 152 > 1850 Grimbergen > > Tel : +32 479 339 655 > Email: [email protected] > > Thank you! I will omit the losetup step. -- Mr. Teo En Ming (Zhang Enming) Dip(Mechatronics) BEng(Hons)(Mechanical Engineering) Alma Maters: (1) Singapore Polytechnic (2) National University of Singapore My Primary Blog: http://teo-en-ming-aka-zhang-enming.blogspot.com My Secondary Blog: http://enmingteo.wordpress.com My Youtube videos: http://www.youtube.com/user/enmingteo Email: [email protected] Mobile Phone (Starhub Prepaid): +65-8369-2618 Street: Bedok Reservoir Road Country: Singapore
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