Disk cloning is the process of duplicating all data on a

digital storage Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, Phonograph record, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA ...

drive, such as a

hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...

solid state drive A solid-state drive (SSD) is a type of solid-state storage device that uses Integrated circuit, integrated circuits to store data persistence (computer science), persistently. It is sometimes called semiconductor storage device, solid-stat ...

, using hardware or software techniques. Unlike file copying, disk cloning also duplicates the filesystems, partitions, drive meta data and

slack space In computer storage, fragmentation is a phenomenon in the computer system which involves the distribution of data in to smaller pieces which storage space, such as computer memory or a hard drive, is used inefficiently, reducing capacity or perfo ...

on the drive. Common reasons for cloning a drive include; data backup and recovery; duplicating a computer's configuration for mass deployment and for preserving data for

digital forensics Digital forensics (sometimes known as digital forensic science) is a branch of forensic science encompassing the recovery, investigation, examination, and analysis of material found in digital devices, often in relation to mobile devices and com ...

purposes. Drive cloning can be used in conjunction with drive imaging where the cloned data is saved to one or more files on another drive rather than copied directly to another drive.

Background

Disk cloning occurs by copying the contents of a drive called the source drive. While called "disk cloning", any type of storage medium that connects to the computer via

USB Universal Serial Bus (USB) is an industry standard, developed by USB Implementers Forum (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical ...

NVMe NVM Express (NVMe) or Non-Volatile Memory Host Controller Interface Specification (NVMHCIS) is an open, logical-device interface specification for accessing a computer's non-volatile storage media usually attached via the PCI Express bus. The in ...

SATA SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard ...

can be cloned. A small amount of data is read and then held in the computer's memory. The data is then either written directly to another (destination) drive or to a

disk image A disk image is a snapshot of a storage device's content typically stored in a file on another storage device. Traditionally, a disk image was relatively large because it was a bit-by-bit copy of every storage location of a device (i.e. every ...

. Typically, the destination drive is connected to a computer (Fig. 1). Once connected, a disk cloner is used to perform the clone itself. A hardware-based drive cloner can be used which does not require a computer. However, software cloners tend to allow for greater flexibility because they can exclude unwanted data from being duplicated reducing cloning time. For example, the filesystem and partitions can be resized by the software allowing data to be cloned to a drive equal to or greater than the total used space. Most hardware-based cloners typically require for the destination drive to be the same size as the source drive even if only a fraction of the space is used. Some hardware cloners can clone only the used space but tend to be much more expensive.

Applications

Deployment

A common use of disk cloning is for deployment. For example, a group of computers with similar hardware can be set up much quicker by cloning the configuration. In educational institutions, students are typically expected to experiment with computers to learn. Disk cloning can be used to help keep computers clean and configured correctly. Further, while installing the operating system is quick, installation of programs and ensuring a consistent configuration is time consuming. Thus, disk cloning seeks to mitigate this administrative challenge.

Digital forensics

One of the most common applications of disk cloning is for digital forensics purposes. This aims to ensure that data is preserved at the time it was acquired for later analysis. Techniques for cloning a disk for forensic purposes differ from cloning a drive for other purposes. Typically, the cloning process itself must not interfere with the data. Because software cannot be installed on the system, a hardware-based cloner is generally used to duplicate the data to another drive or image. Further, the hardware-based cloner also has write-blocking capabilities which intercepts write commands to prevent data being written to the drive.

Backup

Disk cloning can be used as a backup solution by creating a duplicate of data as it existed when the clone was started. The clone can be used to restore corrupted files such as corrupted databases. In modern software solutions, it is not uncommon for disk cloning techniques to be combined with

disk imaging A disk image is a snapshot of a storage device's content typically stored in a file on another storage device. Traditionally, a disk image was relatively large because it was a bit-by-bit copy of every storage location of a device (i.e. every ...

techniques to create a backup solution.

Drive upgrade

Upgrading to a larger or faster drive can be facilitated by cloning the old drive to the new drive once it is installed into the system. This reduces the need to having to manually reinstall applications, drivers and the operating system. The procedure can be used when migrating from mechanical

hard disk drives A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...

solid state drives A solid-state drive (SSD) is a type of solid-state storage device that uses integrated circuits to store data persistently. It is sometimes called semiconductor storage device, solid-state device, or solid-state disk. SSDs rely on non-v ...

. Modern cloning software tends to communicate with storage devices through a common interface, which means, that any storage device can be cloned and migrated. Sometimes, booting from the destination drive can fail and require adjustments in the computer's UEFI or BIOS to make the new clone bootable.

Technical challenges

There are several technical challenges that need to be considered when planning to clone a drive.

Drive in use

Often, cloning software runs within the

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

which is running off of one of the drives being cloned. As a result, any attempt to clone the contents of the drive, even to a file, would result in

data corruption Data corruption refers to errors in computer data that occur during writing, reading, storage, transmission, or processing, which introduce unintended changes to the original data. Computer, transmission, and storage systems use a number of meas ...

. Consequently, the drive cloner must ensure that the data on the source drive remains in a consistent state at the time of reading. Further, in the case, that the user desires to clone to the computer's system drive, this generally cannot be done while the operating system is running. A common solution to cloning a drive that is in use, which is utilized by software such as CloneZilla, is to boot from a Linux-based operating system so the drive can be copied and/or overwritten. This approach is not suitable for servers that need to be running all the time and cannot be shutdown routinely to perform the backup (or cloning) operation. Further, the Linux-based operating system must provide appropriate drivers for the system's hardware. Drivers are also required for the source and destination drives and for any attached storage involved in facilitating the cloning operation such as USB, tape device and networking drivers. Some server-based operating system incorporate mechanisms to allow the drive to be safely backed up while the system is running to overcome these challenges. For example,

Windows Server 2003 Windows Server 2003, codenamed "Whistler Server", is the sixth major version of the Windows NT operating system produced by Microsoft and the first server version to be released under the Windows Server brand name. It is part of the Windows NT ...

(and later) includes volume shadow service (VSS). VSS takes a snapshot of the drive so that any changes are not written to the snapshot.Leschke, T. R. (2010)
Shadow volume trash: $ Recycle. Bin forensics for Windows 7 and Windows Vista shadow volumes
The snapshot creates a virtual drive called a shadow volume that is backed up (or cloned) by the software.

Slow

Disk cloning can be time consuming, especially, for large disks because a true clone needs to copy all the data on the disk even if most data resides in unallocated drive space. Software solutions can determine the space in use and only copy the used data reducing the time needed to clone the drive. Some drive cloners make use of multithreading to further speed up the cloning operation.

References

{{Backup software Storage software Backup Utility software types