Frequently Asked Questions

How does device-image compare to partitionimage project?
If hdb is 20GB but with 80% free space, what image size can we expect?
My hda is 75GB large but i use only 5% of the space, is it possible to exclude empty blocks from the backup file?
When you backup the partition only then you have problem booting, why?
I have a SATA RAID device that can be mounted as /dev/sda*, will it work with zsplit/unzsplit?
You refer in your documentation to Knoppix live CD, I cannot find neither zsplit nor unzsplit there, why?
Does zsplit/unzsplit support backing up and restore to/from a usb drive?

Q1. How does deviceimage compare to partitionImage project?

A: The main difference is the following: partimage analyses and operates on the file-system level, device-image instead, operates on the device level. Therefore the advantage of partimage lies in the possibility to to read out the information only from used blocks making a very small image. The disadvantage is if the file system structure (as in case of NTFS) is not completely known, the support of this file system remains permanent experimental. Consequently you are not sure if your backup image is restorable. The operation mode of device-image is copying byte-by-byte, it means all sectors, regardless of containing or not any data, will be stored in one image. In this case the big advantage is independence from the file-system. Because we save really all data, as additional positive effect here we have a following one: if you want undelete some data which you deleted just before your last imaging it is also possible in contrast to partimage-method. The disadvantage of device-image method is: for restoring you need a device which is the same or bigger in size than original one.

Q2. If hdb is 20GB but with 80% free space, what image size can we expect?

A: Generally the size of image is dependent on the compression rate you choose for zsplit. More compression means smaller image size. But different file-systems could be more or less good compressed. For example FAT file-system could be compressed to 40%-50% of the original size, NTFS file-system is instead less compressive.

Q3. My hda is 75GB large but i use only 5% of the space, is it possible to exclude empty blocks from the backup file?

A: No at this time not, please see comparison to partimage.

Q4. When you backup the partition only then you have problem booting, why?

A: The zsplit does only what it is asking for. So if you makes an image of the partition you have only this partition saved, not the master boot record (MBR) of the device. MBR will be saved only if you make an image of the whole device. Therefore after the restoring only a partition, this partition cannot be found by BIOS without MBR (in case if restoration goes to a new device). The functionality to store separately the MBR is not implemented yet but will be implemented in the future releases. Alternative way to store the MBR is as follows:
Backup MBR:
dd if=/dev/hda of=backup_hda.mbr count=1 bs=512
Restore MBR:
dd if= backup_hda.mbr of=/dev/hda

Q5. I have a SATA RAID device that can be mounted as /dev/sda*, will it work with zsplit/unzsplit?

A: Yes, all devices which could be recognized by the kernel as block devices should work with zsplit/unzsplit.

Q6. You refer in your documentation to Knoppix CD, I cannot find neither zsplit nor unzsplit there, why?

A: Neither zsplit nor unzsplit are yet included in the distribution of Knoppix CD. The only way still to have a possibility to work with these tools is, after booting Knoppix CD, to bring these tools into the Knoppix environment with a help of floppy, ftp, smbmount or nfs. Another opportunity to use zsplit/unzsplit from the bootable LiveCD is the DeviceImage-LiveCD.

Q7. Does zsplit/unzsplit support backing up and rstore to/from a usb drive?

A: Yes, please see the answer for SATA RAID device.