alignment on disk

Question

testDisk 6.14, Data Recovery Utility, July 2013
Christophe GRENIER <grenier@cgsecurity.org>
http://www.cgsecurity.org

Disk /dev/sda - 1000 GB / 931 GiB -

>

CHS 121601 255 63


Current partition structure:
     Partition                  Start        End    Size in sectors

 1 P EFI System                  2048     739327     737280 [EFI system partitio
No FAT, NTFS, ext2, JFS, Reiser, cramfs or XFS marker
 2 P MS Reserved               739328    1001471     262144 [Microsoft reserved
 2 P MS Reserved               739328    1001471     262144 [Microsoft reserved
 3 P MS Data                  1001472  996279870  995278399 [Basic data partitio
 4 P Unknown               1928501248 1930250239    1748992 [Basic data partitio
 5 P Unknown               1930250240 1953523711   23273472 [Basic data partitio
 6 P Unknown                996280320 1920266239  923985920
 7 P Linux Swap            1920266240 1928501247    8235008

As far as I understand my CHS is wrong; it should be 64 or higher.

How to safely edit this ?

Answer 1

The cylinder/head/sector system is not used on GPT disks (with one partial exception; see below), which your disk appears to be. The fact that TestDisk is reporting CHS values on the disk is a less-than-helpful throwback to the old days. You should ignore that value and not worry about it. You can read more about GPT data structures on its Wikipedia page.. You'll note that all the important data structures use logical block address (LBA) values, not CHS values. The only exception is in the protective MBR, which uses the MBR format as a way to keep GPT-unaware tools from mucking with the disk, and therefore includes both CHS and LBA values. The CHS values are ignored by most tools, though, and some GPT partitioning tools put bizarre and nonsensical values in the protective MBR's CHS fields. Thus, even for this minor case, the CHS geometry of the disk is unimportant.