Clonezilla stopped. Can "sgdisk -z /dev/sdx" destroy all the data on sda?

I need suggestions.I wanted to backup sda2 on which Win7 is installed.I deleted the Recovery Resion.(Probably Testdisk can restore this partition because I haven't done any manipulation on that area since then.) Clonezilla said :

This disk contains mismatched GPT and MBR partition: /dev/sdaIt will confuse Clonezilla and might make the saved image useless orfail to clone the disk.You can use gdisk or sgdisk to fix this issue. E.g. if you are sureonly MBR partition table is the one you want, you can run this commandto destroy the GPT partition table while keep the MBR partition table:sudo sgdisk -z /dev/sdx//NOTE// (1) Replace /dev/sdx with the above hard drive name. (2) ALL EXISTING DATA ON THE DISK WILL BE LOST IF GIVING WRONG COMMAND. USE THIS COMMAND CAREFULLY!Please fix this issue then restart Clonezilla again.

So I'm thinking about doing this command,though before doing this I guess I should backup sda by dd in case of accident.And I don't remember whether my laptop had initially a MBR or GTP partition table.

And Win7 don't boot.I tried to restore the MBR and the PBR of Win7 by Windows PE also.

bootsect /nt60 c: /mbrbootsect /nt60 c:

Both command worked fine.But even after that, Win7 didn't boot./Boot/BCD and bootmgr.exe.mui already existed.

I intend to backup sda so that the generated image incldes the area enough beyond the end of sda2,

dd if=/dev/sda of=./sda_60G.img bs=32M count=1920 conv=noerror 

(First I tried

dd if=/dev/sda bs=32M | lzma > /media/SSD_1/sda.img

,but this takes too long time.It takes about 17 minutes per 1GiB.)

When I enter the command

sgdisk -z /dev/sdx

as it is, is there any possibility that all the data on sda will be lost ?And if I destory all the data on sda by sgdisk, can I restore the present state of my HDD using this sda_60G.img ?

And I read the following Q&A.

Clonezilla fails at cloning with mismatched GPT and MBR partition

enter gdisk, type x to enter the experts' menu, type p, type o, and then type q to quit.

I tried to execute this command.But,there came the following message.

# gdisk /dev/sdaGPT fdisk (gdisk) version 0.8.5Caution: invalid main GPT header, but valid backup; regenerating main headerfrom backup!Caution! After loading partitions, the CRC doesn't check out!Warning! Main partition table CRC mismatch! Loaded backup partition tableinstead of main partition table!Warning! One or more CRCs don't match. You should repair the disk!Partition table scan:MBR: MBR onlyBSD: not presentAPM: not presentGPT: damagedFound valid MBR and corrupt GPT. Which do you want to use? (Using theGPT MAY permit recovery of GPT data.) 1 - MBR 2 - GPT 3 - Create blank GPTYour answer:

Which should I choose ?If I choose 2-GPT,
are there any possibility that all data on sda will be lost ?

Additional info.

# fdisk -l /dev/sdaWARNING: GPT (GUID Partition Table) detected on '/dev/sda'! The utilfdisk doesn't support GPT. Use GNU Parted.Disk /dev/sda: 640.1 GB, 640135028736 bytes255 heads, 63 sectors/track, 77825 cylinders, total 1250263728 sectorsUnits = sectors of 1 * 512 = 512 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisk identifier: xxxxxxxxxxDevice Boot      Start         End      Blocks   Id  System/dev/sda1      1250058240  1250263039      102400   83  Linux/dev/sda2        30926848   109707263    39390208    7  HPFS/NTFS/exFATPartition table entries are not in disk order

I've made this sad1 to install Grub a few days ago.

And in the end, after dding sda2 I tried "sgdisk -z /dev/sda" copied and pasted. It succeeded ? sda2 and sda1 are both safe.

# sgdisk -z /dev/sdaCaution: invalid main GPT header, but valid         backup; regenerating main header from backup!Caution! After loading partitions, the CRC doesn't check out!Warning! Main partition table CRC mismatch!         Loaded backup partition tableinstead of main partition table!Warning! One or more CRCs don't match. You should repair the disk!Invalid partition data!GPT data structures destroyed! You may now partition the disk using fdisk or other utilities.

And this time Clonezilla succeeded.I could get the backup image of sda2.But Win7 still don't boot.I've posted this problem.

Where is the HDD driver needed to detect Win7?