Full Image of internal HDD, drive - dd / dd_rescue - with TrueCrypt [bad sectors] [read error]

**Background** I had a problem under Windows with ndis.sys [sys don't start] *Status: 0xc00000e9 Info: Windows failed to load because a critical system driver...* To repair I had to fully decrypt drive [encrypted with TrueCrypt]. Encryption was running fine, but at some point it found a bad sector. At some point it slowed down decryption process significantly. As I was thinking it's a disk problem - I did a search and came across - option to do a full drive backup with Linux **dd** command. That supposed to give me image of whole HDD drive in case of ongoing corruption and possibility to run decryption from different drive. Lenovo G500s **What I did so far** sudo mkdir /mnt/usb sudo mount /dev/sdb2 /mnt/usb sudo chmod -R 777 /mnt/usb sudo dd if=/dev/sda of=/mnt/usb/image.dd conv=noerror The result being dd: error reading '/dev/sda': Input/output error 254256+0 records in 254256+0 records out I have just noticed I can do image trough Disks [I work on latest Knoppix DVD], but didn't try it yet. Also I was getting suggestions that I can use dd_rescue, but has heard it is not exactly safe to the data on drive as it over-writes bad blocks? And didn't try it yet. I'm stuck, please help, I don't have a full backup of latest work from my sys partition, although seems that sda3 / sda5 was fully decrypted.