Data recovery is the process of salvaging data from damaged, failed, wrecked or inaccessible primary storage media when it cannot be accessed normally. Often the data is being salvaged from storage media formats such as hard disk drive, storage tapes, CDs, DVDs, RAID, and other electronics.
This can be due to physical damage to the storage device or logical damage to the file system that prevents it from being mounted by the host operating system. Although there is some confusion as to the term, data recovery can also be the process of recovering deleted information from a storage media in for example forensic purposes.
A wide variety of failures can cause physical damage to storage media. CD-ROMs can have their metallic substrate or dye layer scratched off; hard disks can suffer any of several mechanical failures, such as head crashes and failed motors; tapes can simply break. Physical damage always causes at least some data loss, and in many cases the logical structures of the file system are damaged as well. This causes logical damage that must be dealt with before any files can be rescued from the failed media.
Most physical damage cannot be repaired by end users. For example, opening a hard disk in a normal environment can allow dust to settle on the surface, causing further damage to the platters and complicating the recovery process. Furthermore, end users generally do not have the hardware or technical expertise required to make these repairs; therefore, data recovery companies are consulted. These firms use Class 100 cleanroom facilities to protect the media while repairs are being made. The extracted raw image can be used to reconstruct useable data after any logical damage has been repaired. Once that is complete, the files may be in useable form. Data recovery success rates are just below 100%. Data recovery can even be accomplished for alternate digital media such as Flash cards for digital cameras, old tape drives, etc.
Far more common than physical damage is logical damage to a file system. Logical damage is primarily caused by power outages that prevent file system structures from being completely written to the storage medium, but problems with hardware (especially RAID controllers) and drivers, as well as system crashes, can have the same effect. The result is that the file system is left in an inconsistent state. This can cause a variety of problems, such as strange behavior (e.g., infinitely recursing directories, drives reporting negative amounts of free space), system crashes, or an actual loss of data. Various programs exist to correct these inconsistencies, and most operating systems come with at least a rudimentary repair tool for their native file systems. Linux, for instance, comes with the fsck utility, Mac OS X has Disk Utility and Microsoft Windows provides chkdsk. Third-party utilities are also available, and some can produce superior results by recovering data even when the disk cannot be recognized by the operating system’s repair utility.
Two main techniques are used by these repair programs. The first, consistency checking, involves scanning the logical structure of the disk and checking to make sure that it is consistent with its specification. For instance, in most file systems, a directory must have at least two entries: a dot (.) entry that points to itself, and a dot-dot (..) entry that points to its parent. A file system repair program can read each directory and make sure that these entries exist and point to the correct directories. If they do not, an error message can be printed and the problem corrected. Both chkdsk and fsck work in this fashion. This strategy suffers from a major problem, however; if the file system is sufficiently damaged, the consistency check can fail completely. In this case, the repair program may crash trying to deal with the mangled input, or it may not recognize the drive as having a valid file system at all.
The second technique for file system repair is to assume very little about the state of the file system to be analyzed, and using any hints that any undamaged file system structures might provide, rebuild the file system from scratch. This strategy involves scanning the entire drive and making note of all file system structures and possible file boundaries, then trying to match what was located to the specifications of a working file system. Some third-party programs use this technique, which is notably slower than consistency checking. It can, however, recover data even when the logical structures are almost completely destroyed. This technique generally does not repair the underlying file system, but merely allows for data to be extracted from it to another storage device.
While most logical damage can be either repaired or worked around using these two techniques, data recovery software can never guarantee that no data loss will occur. For instance, in the FAT file system, when two files claim to share the same allocation unit (“cross-linked”), data loss for one of the files is essentially guaranteed.
The increased use of journaling file systems, such as NTFS 5.0, ext3, and XFS, is likely to reduce the incidence of logical damage. These file systems can always be “rolled back” to a consistent state, which means that the only data likely to be lost is what was in the drive’s cache at the time of the system failure. However, regular system maintenance should still include the use of a consistency checker. This can protect both against bugs in the file system software and latent incompatibilities in the design of the storage hardware. One such incompatibility is the result of the disk controller reporting that file system structures have been saved to the disk when it has not actually occurred. This can often occur if the drive stores data in its write cache, then claims it has been written to the disk. If power is lost, and this data contains file system structures, the file system may be left in an inconsistent state such that the journal itself is damaged or incomplete. One solution to this problem is to use hardware that does not report data as written until it actually is written. Another is using disk controllers equipped with a battery backup so that the waiting data can be written when power is restored. Finally, the entire system can be equipped with a battery backup (see UPS) that may make it possible to keep the system on in such situations, or at least to give enough time to shut down properly.
Some kinds of logical damage can be mistakingly attributed to physical damage. For instance, when a hard drive’s read/write head begins to click, most end-users will associate this with internal physical damage. This is not always the case, however. Often, either the firmware on the platters or the controller card will instead need to be rebuilt. Once the firmware on either of these two devices is restored, the drive will be back in shape and the data accessible
Our Denver Data Recovery capabilities:
HARD DISK DRIVES
EIDE and IDE drives using 2.5″ laptop and 3.5″ Normal 40 pin ATA through Ultra ATA/66 interfaces from all manufacturers including:
Areal, CDC, Compaq, Conner, Digital, Fuji, Fujitsu, Hitachi, IBM, Imprimis, Integral Peripherals, JTS, JVC, Kalok, Maxtor, Micropolis, Miniscribe, NEC, Plus, Priam, Quantum, Samsung, Seagate, TEAC, Toshiba, Western Digital, Xebec.
SCSI drives using Normal SE, UW, Differential (WD), LVD, Hot Swappable (SCA) and 2.5″ laptop interfaces from all manufacturers including:
CDC, Compaq, Conner, Digital, Epson, Fujitsu, Hitachi, Hewlett-Packard, IBM, Imprimis, Maxtor, Micropolis, NEC, Quantum, Rodime, Samsung, Seagate, Toshiba, Western Digital.
ESDI, RLL and ST/MFM drives from all manufacturers including: Conner, Digital, Fuji, Fujitsu, IBM, JTS, Kalok, Kyocera, LaPine, Maxtor, Micropolis, Microscience, Miniscribe, NEC, Priam, Quantum, Seagate, Tandon, Toshiba, Tulin, Western Digital.
MCA drives from IBM, Western Digital and Seagate with IBM ST-506 and ESDI and 2.5″ laptop ESDI interfaces.
PCMCIA Type I, II, III hard drives from IBM, Western Digital, Integral Peripherals and Procomm.
CF+ Type II IBM Microdrives
- Compact Flash card, CF card recovery
- Memory Stick, Memory Stick Duo, Memory Stick Pro, Memory Stick Pro Duo recovery
- Secure Digital card, SD card, miniSD, MicroSD card recovery
- MultiMedia card, MMC card recovery
- SmartMedia, SM card recovery
- xD Picture card recovery
- Micro Drive, MicroDrive recovery
- Cellular phone, PDA, MP3 and MP4 player digital media recovery
- Diskettes in 3.5″ format with 720Kb and 1.44Mb, 5.25″ format single and double sided to 1.2Mb capacity.
- CD ROM, CD R/W and DVD R/W disks.
- ISO Optical Formats 3.5″: 128Mb, 230Mb and 640Mb, 5.25″: 1.0Gb, 1.2Gb, 2.3Gb, 2.6Gb WORM and R/W cartridges, including multi-cartridge Jukebox storage systems.
- Panasonic Optical 1.5Gb
- Pinnacle Optical 4.6Gb
- Imation SuperDisks 120Mb
- Iomega ZIP disks 100Mb and 250Mb
- Bernoulli 44Mb, 90Mb, 105Mb & 150Mb 5.25″ cartridges, JAZZ 1Gb and 2Gb
- Syquest 5.25″ cartridges 44Mb, 88Mb and 200Mb, 3.5″ cartridges 135Mb, 230Mb and 270Mb
- SPARQ 1.0Gb and SYJET 1.5Gb cartridges, ORB 2.2Gb cartridges
- 4mm DAT format including DDS, DDS-2 and DDS-3 tapes up to 24Gb capacity.
- 8mm Exabyte Digital tape including 112m and 160m tapes.
- Quantum DLT III and DLT IV tapes up to 80Gb capacity.
- Seagate AIT tapes up to 50GB capacity.
- OnStream ADR tapes up to 50Gb capacity.
- Travan TR-4 8Gb QIC tapes.
- Iomega Ditto 2Gb QIC tapes.
- QIC DC600 series tapes up to 4Gb capacity.
- QIC Mini-Cartridges DC2000-DC2120 with 40 to 80Mb capacity.
- Windows 2000, Windows XP, and Windows Server with Dynamic file system, NTFS, FAT32, FAT16 file systems using standalone, spanned, striped or fault-tolerant RAID volumes.
- Windows NT Workstation and Server with NTFS, FAT32, or FAT16 file systems using standalone, spanned, striped or fault-tolerant RAID volumes.
- Windows 98/95 with FAT32 or FAT16 file systems and long filenames.
- MS-DOS and variants using 12 or 16 bit FAT file systems.
- Compressed volume managers including Stacker, DoubleSpace, and DriveSpace.
- OS/2 with FAT and HPFS file systems.
- Novell NetWare with FAT and NSS files systems using standalone, spanned, striped or fault-tolerant (RAID) volumes.
UNIX OPERATING SYSTEMS
- SCO OpenServer and Xenix
- UnixWare from Novell & SCO
- Linux (all distributions)
- Apple Macintosh with HFS and HFS+ file systems, including fault-tolerant (RAID) volumes.
- Solaris on Sun/SPARC workstations including fault-tolerant (RAID) volumes.
- HP-UX on Hewlett-Packard workstations including LVM volumes.
- IRIX on SGI workstations.
- AIX on IBM RS/6000 workstations including LVM volumes