ARCserve Backup Format

In 1990 Cheyenne Software created the client/server backup software suite called ARCserve allowing backup storage solution for networked computers. Designed to provide a Hierarchical Storage Management (HSM) solution across a wide range of platforms, it was possible to back data up to the storage media of your choice such as tape or optical disk.

Over the last twenty five years ARCserve has undergone a large amount of development and now provide unified data protection servers as their data backup solution. As with the original software data can be easily backed up from a wide range of computers and servers, also providing virtual server support, data deduplication services, mirroring and automated failover server systems. The core of ARCserve is to provide data backup and a means of recovering data in the event of a disaster.

History of ARCserve History

Aimed primarily at the enterprise market, Cheyenne Software developed their flagship product ARCserve as a server based software solution to allow data on a network to backed up to the client’s media of choice. The importance of data backup solutions was soon apparent with OEM’s distributing copies of the software in 1993, ensuring ARCserve was seen as one of the most important data backup software suites. This enabled them to release versions aimed at specifically at the Windows and Apple Mac markets, providing standalone software solutions.

Computer Associates acquired Cheyenne Software in 1996 which allowed ARCserve to be developed across an even larger range of platforms. In 2014 Marlin Equity Partners purchased ARCserve, turning it in an independent company providing full disaster recovery services.

Format of ARCserve Backup

Cheyenne Software created a propriety data format for all its ARCserve products, the details of which have not been made publicly available. The data format is however highly structured making it relatively simple for our tape data recovery research and software development team to determine the metadata structures. This makes it possible to perform data recovery from any ARCserve backup, be it a complete or partial backup.

ARCserve maintains a database on the computer rather than storing an on-tape copy as some other software does. If the catalogue needs to be recreated the tape backup sets can be rescanned. This allows selective restores to be made using the ARCserve software suite.

ARCserve and Data Recovery

A wide variety of tape media can be used with ARCserve with data coming from a vast range of different source computers, from which DiskEng are able to recover the files or provide data conversion services. We can recover and restore your files, whether the backup is incomplete, such as a damaged, overwritten or missing tape or the backup sets have logical corruption making the data inaccessible to the ARCserve software.

The most common reason for a tape containing an ARCserve backup to require data recovery is due to a physical media issue or user errors, such as a tangled and snapped tapes, reinitialising or overwriting a previous backup. At one time problems with tape driver support, particularly on Windows systems were a common problem, which could lead to the incorrect format being written to the tape media were fairly common, such an occurrence is rare, although not unheard of, especially if attempting to restore from old archive media.

Quarter Inch Cartridges (QIC) and Travan

Quarter inch cartridges (QIC) often called “quick” were developed by 3M in 1972, mainly for use on mainframe and mini-computer systems. All quarter inch cartridges store data using the linear serpentine recording format with the read/write head moved up and down using a servo motor. The tape is advanced at a constant speed using a continuous belt which is in direct contact with both tape spools and a drive wheel which is driven directly using a capstan.

Quarter inch cartridges are often referred to as metal backed tapes due to the thick aluminium baseplate which is common to each tape. Following the development of the Personal Computer (PC) a smaller version was developed, aimed particularly at small businesses and home users, called the Mini-QIC tape (using 8mm wide tape) which used the floppy drive interface. In 1992 in order to increase the available capacity on Mini-QIC tapes, 3M developed the Travan cartridge range which uses media 8mm wide. These are now all obsolete tape cartridges, but examples are still in use or hold important data, so there is still a requirement for data recovery.

Quarter Inch Cartridge Design

A solid metal baseplate usually made of aluminium forms the base of the tape cartridge providing rigidity. The two tape media spools are located upon two pins solidity fixed to the baseplate, with further guide pins and the drive wheel also attached to the baseplate. A wheel inside the drive mechanism directly contacts the tape cartridge drive wheel, which in turn moves a rubber band which moves the tape spools through direct contact.

Unlike many other tape formats, the tape media is not physical affixed to the tape spools. A series of holes at specific intervals on the tape are used to detect the end of media in both directions, which are detected via a 45 degree mirror onto which light is shone. The cover over the tape is a plastic shell, which in general translucent with the Travan range being the main exception. Unlike DLT and LTO media, the data is recorded in a genuine serpentine fashion, with the first track generally being at the bottom edge of the media.

QIC Storage Capabilities

The first QIC tape format released in 1972 was the DC300 which contained 300 feet of tape and capable of storing 200 kilobytes of data. Over the years the number of tracks was increased along with the length of the tape and the magnetic density of the media, allowing a significant increase in the storage capacity. The last generation the Scalable Linear Recording (SLR) tapes developed by Tandberg in 2005 are capable of storing 70GB of raw data.

The mini-QIC cartridge drives developed to fit into a 3.5 inch drive bay were initially capable of storing 40MB on a DC2000 using the QIC-40 format. The QIC-80 format allowed a further increase but it was the development of the Travan series by 3M which allowed a significant rise in storage capacity. The Travan TR-1 was capable of recording 400MB when it was released in 1995. The TR-7 was the final generation which was released in 2002 and capable of storing 20GB. Iomega released a similar series of tape cartridges based on the same form factor, the Ditto and DittoMax data cartridges, using a proprietary format. HP Colorado drives also used a proprietary version of the Travan format.

QIC/Traven Problems and Data Recovery

The rubber belt used for transferring the tape between the two spools can cause problems, particularly in the mini-QIC cartridges. The biggest problem is due to the belt being liable to slippage which can cause either the tape to move up or down, leading to uneven winding, or worse result in the tension of the tape to either increasing or decreasing. If the tape becomes unevenly wound, it can cause the tape to rub on the case, which may lead to resistance, and in the worst cases the tape drive capstan can damage the drive wheel in the tape cartridge. If the media tension increases it may lead to the tape becoming stretched, which can lead to alignment problems in that section of the tape. If the media tension decreases however, the result can lead to the tape becoming creased, or in the worst case become tangled around something it shouldn’t. Such a situation can rapidly destroy a large section of the tape.

The common issue we seen with QIC and Travan tape cartridges is where the tape have unspooled at one end. This can happen due to a failure of the sensor, damage to the alignments holes in the tape media or damage to the mirror. It is quite common to attempt a repair when this occurs, but these have been seen in many cases to cause huge problems, especially if the media is physically attached with sticky tape to the spool. If this is done and the drive again fails to detect the end of the media, it will attempt to continue spooling the tape, which will then cause tape to be forcibly removed from full spool, which will cause a large section of the tape to become tangled. Data recovery and data conversion from these types of data cartridge should only be undertaken by a professional data recovery company with extensive knowledge and experience.

Tar Backup Format

Tar is a software utility used for collecting multiple files in a single archive file, sometimes referred to as a tarball. The name is derived from tape archive, originally designed for writing data sequentially to a tape drive. Historically early tape drives wrote variable length data blocks, which is slower and less efficient than writing fixed length blocks. Tar was designed for writing fixed length data blocks, allowing file headers to have a fixed alignment, allowing backups to be created to tape, disks and files.

Originally tar was developed within the Unix environment as a means of creating archives which could be used for data backups and as a means of distributing data. In line with all successive backup formats all data headers contain the relevant metadata associated for each file which is stored in the archive. Tar has a long history with many extensions added, but is a very well-known format, which makes data recovery a relatively easy task.

Tar Development

Headers within the original tar archive format used printable octal representations of all numbers, which for historical reasons limited the maximum size of any individual file stored within the archive to be 8GB. In 2001 the ability to store number in native binary format which potentially allows files of unlimited size and larger than the current 64 bit limitation present within most file systems to be archived.

Through a process of proposals and ratification through a POSIX standard, other limitations have been overcome, such as dates extended from 32 bit representations to 64 bit allowing nanosecond resolution, now common with most operating systems and data volumes. Security information was limited to the standard Unix permissions, user id and group id. This has been extended to allow extended attributes and access control lists (ACLs) to be stored.

Tar Archive Usage

Although tar archives are now rarely used for backing up data to tape, they are very commonly used for distributing software and updates. It is also common to combine one of many compression formats available on Unix systems, with the tar archive, whereby the archive stream is compressed as it is created.

The tar archive utility available on Unix systems is a command line tool, with no graphical user interface, with no ability for creating a catalog of files written to tape. It is therefore not ideal as part of a backup strategy within a disaster recovery plan. However tar has also formed the basis for several backup packages which have strived to overcome this limitation, providing a graphical user interface, in order to allow easy selection of which files should be backed up or restored. One such utility is Veritas NetBackup which provides cross-platform backup functionality, allowing multiple computers to send data to a single server.

Tar Data Recovery

Although tar is now rarely seen especially on modern tape drives, it can still be found on some older and no obsolete tape formats, such as Exabyte tapes, early DDS dat cartridges and any other tape drive commonly used with a Unix system.

Tar is an important data format, as it is in common use for software distribution, particularly in the open source sector, as well as the core for many other backup formats still in use. It is also useful for recovering or converting data stored as a tar archive on legacy tape data cartridges.

IBM 3480 3490E 3590 3592 Data Cartridges

A core business area for IBM is providing enterprise solutions using mainframe and server systems. For many years the solutions ranged across many different architectures, most proprietary to the operating system. As part of the solution IBM also developed a range of tape technology, including tape libraries for performing data backups. In 2001 IBM unified much of their server technology, introducing the Z Series of servers using 64 bit architecture, at the same time replacing OS/390 with z/OS as the preferred mainframe operating system. The Z Series server has been designed to also allow Linux to be installed.

IBM have developed many tape drives and tape media designed to serve as a backup solution on their own servers and any other system with the appropriate SCSI interface installed. All these tape drives have been based on the same linear recording principle as the half inch open reel technology, which are often used in movies when a large computer needs to be indicated. These enterprise level tapes are rarely seen for tape data recovery, largely due to the diligence used in ensuring multiple copies of the same data are backed up. We do however see many enquiries requesting tape data conversion, either to make duplicates for distribution, or to change tape or backup format.

3480 and 3590E Data Cartridges

These data cartridges incorporate a single half inch tape spool encased with in a plastic shell with the dimensions 4”x5”x1”. Data is recorded on multiple tracks across the tape simultaneously making a single pass in to the end of the tape, before recording data in the reverse direction, which significantly reduces the number of tape passes required over formats such as the DLT and LTO data cartridges. These tapes are popular for use with robotic tape libraries, which is possible through human and machine readable labels, which later incorporated bar codes, as a more reliable identifier.

When the 3480 was introduced in 1984 it was capable of storing 200MB recording 18 tracks simultaneously. In 1986 hardware based compression was introduced, doubling the capacity to 400MB. For companies creating large amounts of data, such as those undertaking geophysical surveys, an increase in capacity was essential. This need was catered for in 1991 through the development of the 3490E data cartridge, which records 36 tracks simultaneously, allowing 800MB of raw data. Hardware compression was added in 1992 which is quoted as increasing the capacity to 2.4GB.

3590 and 3592 Data Cartridges

These use the same form factor as the 3480 data cartridge, allowing an easy transition, as upgrades to robotic libraries were unnecessary. The first 3590 tape drive (B Model), was introduced in 1995, with two types of media available, “High-Performance” and “Extended High-Performance” data cartridges, the latter allowing double the capacity. The B Model allowed up to 20GB to be stored on the extended data cartridge. The E Model introduced in 1999 double this capacity, with a further increase to 60GB using the H Model developed in 2002. All 3590 tape drives and data cartridges are nicknamed Magstar.

The 3592 range, nicknamed Jaguar, superseded the 3590 when it was released in 2003. The first generation increased the native data capacity to 300GB, a significant increase. Subsequent generations of the drive record a different format to the same data cartridge allowing older cartridges to be reused when the drive has been upgraded. The second generation was named TS1120, with subsequent generations changing the second to last digit for consistency. The 5th generation, the TS1150 was introduced in 2015, which allows 10TB of data to be stored on a single data cartridge, with data transfer speeds of up to 300MB/s.

IBM Tape Data Recovery and Conversion

The reliability of these tape drives and data cartridges, as expected with an enterprise solution, is extremely good. The reliability of these tape data cartridges is enhanced by the need for only a single pass to the end of the tape and back to fill it to capacity. As mentioned earlier, it is rare to see one of these data cartridges arrive for data recovery, as problems when they occur, are usually of little significance due to the enterprise culture of regular and multiple backups.

Although some are seen which have developed a physical problem, usually a media flaw, the majority of this type of tape requiring data recovery are due to operator error. This includes reinitialising and overwriting important data. Recovering data from a type of this type which has been overwritten is usually a relatively simple process, which in the case of relabelling or reinitialising a tape leads to only a small loss of data. It is more common for us to see data cartridges of this type which require tape data conversion.

Backup Exec and Microsoft Tape Format

In 1996 Conner was merged with Arcada (a Conner subsidiary) to form Seagate Software when they were acquired by Seagate Technology. A new tape backup format specification was developed called the Microsoft Tape Format (MTF) used in all releases of Backup Exec subsequent to 1998. Microsoft also made use of MTF in Windows NT for NTBackup and subsequent versions of Windows backup software.

The Microsoft Tape Format is also used in Windows BKF files and the BackupAssist utility. The design of the Microsoft Tape Format was formulated to allow the easy interchange of information between different computing platforms. The ability to ignore OS specific data incompatible with the target file system such as Apple data forks was an important aspect of the design. Data recovery and data conversion are often required from tape data cartridges using the Microsoft Tape Format.

History Backup of Exec

MaynStream software was developed in 1982 by Maynard Electronics, which was acquired by the Archive Corp in 1989. Versions of MaynStream were developed for the DOS, Windows, Macintosh, OS/2 and NetWare operating systems. Conner Peripherals acquired Archive Corp in 1993, at which time the software was rebranded as Backup Exec. MaynStream used a proprietary backup format up until Seagate Software was created.

Seagate Backup Exec was marketed in 1998 following the development of the Microsoft Tape Format. In 1999 VERITAS Software acquired Seagate Software before being subsequently acquired by Symantec in 2005, the current owner and developer of Backup Exec. Since it was first developed the format has been expanded such as allowing locked files and databases still being used and updated to be backed up, which is achieved by installing the appropriate backup agent modules.

Microsoft Tape Format (MTF)

The MTF specification document was most recently published released in 1998. Since then many additional developments have been made, specifically for the backup of databases, which have not been documented and proprietary in nature.

Microsoft’s NtBackup and later versions of Windows Backup use MTF which can be restored using Backup Exec. However the reverse is true for simple file backups made using Backup Exec. However any backups made using an agent module with Backup Exec is incompatible with the Windows Backup software.

Backup Exec and Data Recovery

A wide variety of tape media can be used with Backup Exec and Windows Backup. Although the last published specification was in 1998, any additions to the format conformed to the same basic formatting, which allows the extraction of files during data recovery to be a fairly simple process.

There are many typical reasons for requiring data recovery for a backup used the MTF based format are due to a physical media problem or a logical software issue. These can range from a snapped tape, user error through reinitialising or overwriting media, or a logical data issue, which the backup software is unable to handle. DiskEng have vast experience of dealing with such issues, from which data can be extracted and returned.

Tape Data Storage Considerations

For archive and long term storage of digital data it is common practice to use a tape data storage solution. While hard disk drives, USB storage and recordable media have increased in capacity and increasingly reliable, they should not be considered as the best option for long term storage.

It is important though to understand that all tape media has a limited lifespan, mainly dependent upon the environmental conditions of storage and the pattern of usage. The two most common reasons for requiring data recovery from an archive backup tape are through poor storage conditions or due to the tape being overused.

Storage Environment Is Important

As with hard disk drives, it is important that tape data cartridges are stored and used within a certain temperature range, otherwise the lifespan of the media may be significantly reduced. Heat can affect the surface of the media, which can lead to tape becoming sticky, which in extreme circumstances may cause the magnetic recording layer to be damaged. Not only will this cause a problem for the tape media, but may lead to an early failure of the tape drive.

Another important consideration is the location where the tapes are stored. Ideally any tape backup media should be stored off-site, such that in the event of a disaster it will be unaffected and readily available to restore the data. Should you want to store backup on-site, a fireproof safe situated next to an outside wall on the ground floor is the best option. Fireproof safes are however only rated to a certain temperature before the contents will start to suffer damage.

Data Cartridge Cycle

Each tape data cartridge is rated for a certain number of passes before the presences of data errors in the form of media flaws are expected. This is due to the speed at which the read/write heads or the tape move, which will inevitably cause wear and tear. It is therefore important that the tape drive is regularly maintained, as dirt on the read/write heads will further wear and tear.

It is therefore important that new tape data cartridges are regularly introduced into the backup cycle. Some large corporations will only use a brand new tape data cartridge for each backup, whereas many will rotate on a monthly basis. There is no hard and fast rule, but the importance of the data and being able to maintain business continuity will determine how often new data cartridges are used.

Tape Data Recovery and Conversion

With many tape data cartridges having a quoted lifespan of 10 to 15 years, it is easy to see long term data storage on any media is not ensured. For companies who must maintain archive data from which e-disclosure may be required in the future, it is important that it is regularly transferred via tape data conversion to new media to ensure it is secure.

A failure to ensure that archive material is always secure could at a future date cause problems, leading to tape data recovery, which in complex cases may be expensive. It is important not to only think about archive data when it is required, but to ensure that it is always readily available, through regular data conversions. This will ensure that no data is lost through the tape media developing an problem, which would require tape data recovery.

AIT and Super AIT Data Cartridges

Advanced Intelligent Tape (AIT) data cartridges were developed in 1996 by Sony. AIT data cartridges record data onto an 8mm media using the helical scan recording method. Another feature is the Memory In Cassette (MIC) chip which is used to store information about the data recorded on the tape.

The first AIT tape data cartridge had a native storage capacity of 25GB which was further developed with the 5th generation released in 2007 capable of storing 400GB of uncompressed data.  The first Super AIT (SAIT) was released in 2003 with a native capacity of 500GB with the 2nd generation released in 2006 was capable of holding 800GB of uncompressed data, but only available in tape libraries. Sony officially announced the discontinuation of the AIT and SAIT range in 2010. Despite being obsolete some are still in use, mostly for restoring archive data, some of which have required tape data recovery.

Forerunner to AIT

The predecessor to AIT was the Exabyte tape data cartridge, also using 8mm media using the helical scan recording method. The Exabyte tapes were developed using the same technology as 8mm video recorders, engineered to record digital data. Exabyte Mammoth tapes a higher capacity format was introduced by the Exabyte Corporation, but struggled to compete with AIT, despite the release of the Mammoth 2 data cartridge in 1999.

Advanced Tape Technology

All AIT and Super AIT tape data cartridges use media created using the Advanced Metal Evaporation (AME) technique, allowing both higher density and more reliable data recording, when compared to the traditional Metal Particle tapes using in the original Exabyte cartridges.

The MIC chip contains data only for use by the tape drive, with no area for user data as seen in in the LTO memory chip. There is the possibility to create up to 12 partitions on an AIT data cartridge, although in practise most data cartridges only contain a single data area.

AIT and SAIT Data Recovery

The three most common reasons an AIT data cartridge will require tape data recovery is physical failure, logical data issues or user errors. Physical problems include tape media flaws, unreadable media, snapped tape and de-spooled media. Logical issues are related to a corruption of the tape backup or other restore failures.

A user error such as reinitialising the tape will usually result in some loss of data. A backup format which stores a large area of metadata at the front of the tape may however sometimes allow all files to be recovered. Should you overwrite a previous backup this will lead to some loss of data, the extent of which is depends on the amount data written during the original and subsequent backup.

LTO Ultrium Cartridges

Linear Tape Open (LTO) was developed in late the 1990’s for storing data on magnetic tape, using an open standard as an alternative to the many proprietary tape data cartridges. The LTO Consortium created through collaboration between Hewlett-Packard, IBM and Seagate, directs the development and manages all the licences for tape and drive manufacturers.

Ultrium is the name for the standard form-factor for LTO technology, the original version of which was released in 2000, capable of storing of uncompressed data. The LTO 6 data cartridges and drives released in 2012 are able to store 2.5TB of uncompressed data. Initially seen as a high end data storage solution, it is now affordable for small companies to use the older generation of tape cartridges and drives.

Recording Format

The LTO Ultrium was developed to be a replacement for the DLT data cartridge, also using half inch tape, and a similar size of cartridge, to allow easy modification of robotic libraries. Also like the DLT data cartridge, the recording is described as linear serpentine with the data stored in an outward spiral.

An important aspect of the LTO drives are that they are able to vary the speed at which the tape moves across the read/write heads, to alleviate one of the problems which can occur if the data is not being supplied at full bandwidth the drive is capable of writing data at. This cuts the number of times the tape drive is required to stop and reposition for the data write, which reduces the amount of tape ware, and reduces the unnecessary delays this would cause.

LTO in the Future

LTO Ultrium is now the bestselling tape data backup cartridge, having seen development of the DLT and AIT range of drives stopped. Further development of the DAT DDS range of drives and tape cartridge also appears to have come to a halt, leaving LTO as the only high capacity data cartridge still being developed.

The current roadmap for LTO Ultrium development details expected releases through to a 10th generation data cartridge capable of storing 48TB of uncompressed data on a single cartridge.

LTO Data Integrity and Recovery

In common with the DDS DAT recording format, the LTO Ultrium drive immediately reads the data written to tape, in order to verify that it was written correctly, which increases the reliability, but does not exclude the possibility of read errors when attempting to restore a backup. The most common issues requiring data recovery encountered with LTO Ultrium data cartridges, are operator or software related, from re-initialising the tape, overwriting a backup, or logical data corruption of the stored data.

The expected lifetime of an LTO Ultrium data cartridge, used for archival purposes is quoted as 15 to 30 years, which is dependent upon the conditions in which it is stored. Each cartridge is expected to last 5000 load and unload procedures, and approximately 260 full passes (writing or reading to the maximum capacity of the cartridge) before it is expected to fail. With the first tape cartridges released in 2000, any used to archive data may now start to be seen for data recovery from 2015 onwards.

DLT and Super DLT Tapes

Digital Linear Tape (DLT) originally called CompacTape was developed by Digital Equipment Corporation (DEC) from 1984. In 1994 Quantum Corporation purchased the technology, manufacturing drives. Quantum also licenses the technology and trademark.

A higher capacity variant called Super DLT (SDLT) was developed in 1998. Under license from Quantum a budget line was developed by Benchmark in 1999 and later purchased by Quantum in 2002. All tapes cartridges use linear tape recording in a format known as serpentine, although in reality an outward spiral is used. In 2007 Quantum brought the DLT range of tapes cartridges to an end, shifting their tape data storage strategy to LTO Ultrium tape drives and cartridges.

CompacTape and DLT Cartridges

The original CompacTape data cartridges developed by DEC for the TK range of drives had a rough surface, which if placed into a later drive can damage the read/write heads. With the introduction of DLT III media became a practical tape backup solution, mostly used in mainframe and server environments. The DLT2000 drive allowed up to 10GB of uncompressed data to be recorded onto a single cartridge in 1993. After Quantum bought the technology they introduced the DLT2000XT drive and DLT IIIXT media allowing 15GB of uncompressed data to be stored.

The DLT IV data cartridge was introduced in 1994 with the DLT4000 drive, allowing 20GB of uncompressed data to be recorded. 1996 saw the introduction of the DLT7000 drive which allows 35GB to be stored on a DLT IV data cartridge. The DLT8000 drive extended the DLT IV cartridge capacity to 40GB of uncompressed data. The DLT IV data cartridge was also used in the first two budget drives manufactured by Benchmark, also allowing 40GB of uncompressed data to be stored, at a lower data transfer rate, using proprietary format incompatible with the Quantum recording format.  The budget line was extended after the Quantum purchase, allowing 80GB and 160GB on using VS1 media using the DLT-VS160 and DLT-V4 drives respectively.

Super DLT (SDLT)

To extend the storage capacity available, the Super DLT range was created, initially extended the uncompressed capacity to 110GB in 1998, using SDLT 1 media in a SDLT 220 drive, and 160GB in the SDLT 320 drive. The SDLT 600 drive was introduced in 2004, which is able to record 300GB of uncompressed data on SDLT 2 media. The final iteration of the recording format was the DLT-S4 drive manufactured in 2006, is able to store 800GB of uncompressed data onto S4 data cartridges.

DLT Data Recovery and Conversion

Since Quantum brought an end to DLT technology in 2007, the requirement for DLT data recovery has diminished considerably. In spite of this, we still have the knowledge and expertise required to undertake data recovery from any DLT data cartridge.

It is now a legacy media, from which data conversion and electronic disclosure are now the biggest requirement. At DiskEng we have the expertise and experience to recover and convert the data or perform electronic disclosure, whatever the media and backup software used.

DDS DAT Cartridges

Digital Data Storage (DDS) is the recording format used for computer data storage on Digital Audio Tape (DAT) cartridges using the helical scan method. DAT was developed by Sony for recording high quality digital audio recordings, but only saw limited success, mainly in professional studios.

The Digital Data Storage (DDS) format was defined jointly by Sony and Hewlett Packard for recording data to DAT cartridges. The first generation of computer storage media the DDS-1 was introduced in 1987 with an uncompressed data capacity of 1.3GB. DAT data cartridges are always quoted as having a compression ratio of 2:1, but this is dependent upon the data being recorded.

4mm DAT cartridges

The first 5 generations of the DDS DAT data cartridge are labelled as 4mm data tapes, although it is really on 3.81mm wide media. The earliest couple of generations were prone to alignment issues, with the guide pins coming loose and out of alignment, which could cause issues whereby data could not be read back easily. If left unchecked, it could eventually lead to new data tracks overwriting the previously recorded ones, which would cause serious problems during data recovery.

From the DDS-3 tape drive onwards automatic tracking and better guide pin technology was built into the drives, largely eliminating this as an issue. By the time the DAT 72 (sometimes called DDS-5) the 5th generation drive was introduced in 2003, the uncompressed storage capacity had increased from 1.3GB to 36GB on a single data cartridge.

8mm DAT Cartridges

In 2007 Hewlett Packard released the DAT 160 which was developed to use 8mm tape media, allowing for significantly higher storage capacity, in this instance 80GB uncompressed. In 2009 the DAT 320 with double the storage capacity was introduced.

In order to house the larger tape width the cartridge is larger than its 4mm predecessor, although the DAT 160 tape drive provides backwards read/write compatibility with DAT 72 and DDS-4 tapes. The DAT 320 drive is only compatible with its predecessor the DAT 160. The release of the 8th generation has yet to be announced, but a 2012 announcement has planned to be able to store 300GB uncompressed.

DAT Data Recovery

The most common reasons to require data recovery from a DAT data cartridge falls into 3 categories, these being, physical failure, logical data issues or user errors. The physical problems include tape media flaws, unreadable media, snapped tape and de-spooled media. Logical issues relate to corruption of the tape backup and restore failures.

User errors from reinitialising the tape will usually result in some loss of data, although some backup formats which store metadata at the front of the tape, may sometimes allow all files to be recovered. Overwriting a previous backup will lead to some loss of data, the extent of which is totally dependent upon how much data has been backed up.