Hi, I was able to recover recover files through the external hard disk recovery software but could not open the file. Any suggestions please?
Some of the suggestions above are good. Also try these:
* http://sourceforge.net/projects/wordrecovery/ - S2 Recovery Tools for Microsoft Word. Like the Excel one makes easy Microsoft recommended ways of opening corrupt Word files. Also adds own methods.
* http://sourceforge.net/projects/savvyoffice/ - Savvy Office Recovery. Works with DOCX and XLSX only.
* https://online.officerecovery.com/ - do a demo recovery than use the coupon code "S2SERVICES" for free recovery until Nov. 1, 2013.
* http://onlinerecovery.munsoft.com/ - post to Facebook, Twitter or your blog about the service and get 10 free recoveries.
For commercial recovery programs, these companies seem to work well:
* http://www.cimaware.com/main/products/products.php - middle to expensive. Recovers formatting.
* http://www.recoverytoolbox.com/ - inexpensive but no format recovery.
* http://www.munsoft.com/downloads/ - middle to low price. Includes bulk and format recovery.
* http://www.officerecovery.com/ - expensive but recovers formatting. The online file repair service mentioned above with the free S2SERVICES coupon is provided by the same company using presumably the same methods.
what can be recovery success percentage? is it dependent on the recovery software?
Sometimes it is dependent on the software. You just have to try the freeware/open source ones or the demos of the commercial ones. A lot of the commercial ones have batch modes which is convenient. My free ones and the services do not provide batch modes as far as I know.
suppose the hard drive is overwritten after the files are lost, so are the software capable to restore at least partially the files after recovery?
You should know that I'm a bit of a self taught amatuer on this subject after all these years in the data recovery business, but here is my current understanding.
If a part of a of file is truly overwritten, that part cannot be retrieved. If the a cluster (the smallest logical section of storage of a file on a disk - for old disks it was 512 bytes, new ones it is 4096 - that is most new disks by the beginning of 2011) making up part of a file has not been overwritten, but simply marked in the file table as open for overwriting in the future, than yes that part of the file can be recovered.
Partial files can sometimes be useful for data recovery. For instance with Word files of the DOC and DOCX kind, the text in either unzipped or zipped form, resides only in a small portion of the file, and if that part of the file happens to reside on a cluster that has not been overwritten, recovery is possible. For DOC files, the text is simply unencoded text, near the end. For DOCX files it is in a zipped up subfile called document.xml which with a zip repair program can be recovered and or even partially recovered if the subfile has been truncated. I have recovered text from both DOC and DOCX files where part of the file is gone but at least part of the text section is still there.
If a cluster of a file or all the clusters that used to make up a file have been overwritten than the file or any of its parts is most likely unretrievable (see the caveat below). An apparent myth developed was set off by Peter Gutman in a 1996 paper that data was still retrievable on the borders of erased tracks or by subtracting an ideal data signal of what was expected from what was found. Thus was the method of overwriting the disk 35 times born. He argued in the paper that RAM and now presumably SSD's are subject to recoverable data remanence too but for different reasons.
NIST, the National Institute of Standards has more recently found at least with spinning platter drives it may not be necessary to overwrite more than one time. At best a very small fraction of the bytes can be reconstructed from the borders of spinning platter tracks or by the subtraction of actual from the ideal data and only with an electronic microscope or other expensive impractical equipment.
Here is a quote from the Wikipedia article below: "As of November 2007, the United States Department of Defense considers overwriting acceptable for clearing magnetic media within the same security area/zone, but not as a sanitization method. Only degaussing or physical destruction is acceptable for the latter.
On the other hand, according to the 2006 NIST Special Publication 800-88 (p. 7): "Studies have shown that most of today’s media can be effectively cleared by one overwrite" and 'for ATA disk drives manufactured after 2001 (over 15 GB) the terms clearing and purging have converged.' An analysis by Wright et al. of recovery techniques, including magnetic force microscopy, also concludes that a single wipe is all that is required for modern drives. They point out that the long time required for multiple wipes 'has created a situation where many organisations ignore the issue all together – resulting in data leaks and loss. '"
There is one caveat to this, that I think both the spinning platter drives and the SSD's will develop damaged sectors which once detected, they will set aside and not try to use anymore. That data is not erased and theoretically can be recovered. However it probably is most often just parts of files and not enough to do meaningful reconstruction.
There has been a small built-in application in all hard drives made since 2001, which will, when engaged, wipe a hard drive completely clean including those set aside clusters. (I assume for spinning platter drives it overwrites the disk once and for SSD's twice - see below). You can find a piece of freeware, in the link below, that executes that command. As for finding software that will go into set aside damaged clusters and try to retrieve the data on the sectors for you, I haven't come across one yet, but I bet there is one.
So there short answer is for spinning platter drives at least, an actual overwritten cluster or hard drive sectors cannot not be recovered, unless copies have been previously set aside as damaged. For recovering data from those clusters or sectors of the drive you would need special software or even hardware and special training. Partially overwritten files can be recovered if the key data is recovered from non-overwritten clusters. This key data is found in continuous sections of DOC, DOCX, and XLSX (data in XLSX files is split between the numbers found in the worksheet.xml subfiles and the sharedstrings.xml subfile) files.
I'm not an XLS file expert. The text strings are clearly unencoded like with DOC files. However for the numbers may not be as straightforward. There are many commercial programs that clearly understand XLS file structure and can fix corrupt or partial XLS files. Here seems to be a good primer on the subject although I got lost after awhile: http://www.gaia-gis.it/gaia-sins/freexl-1.0.0e-doxy-doc/Format.html.
For SSD here is a quote from experts on the subject and which I found in the Wikipedia article on data remanence linked below: "First, built-in commands are effective, but manufacturers sometimes implement them incorrectly. Second, overwriting the entire visible address space of an SSD twice is usually, but not always, sufficient to sanitize the drive. Third, none of the existing hard drive-oriented techniques for individual file sanitization are effective on SSDs.(p1)"
http://en.wikipedia.org/wiki/Data_remanence - excellent article
http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html - Peter Gutman's paper that initiated strategies of overwriting disks numerous times. Please see the epilogues for more complete and less confident analysis on his part.
http://wayback.archive.org/web/20060210041901/http://shsc.info/DataRecovery - classic article with many resource links for file recovery
[Broken Link Removed] - app that allows you to sanitize drives
http://wiki.lunarsoft.net/wiki/Data_Recovery - excellent article on failing drive recovery
http://ia600600.us.archive.org/22/items/2011-cdc-disk-archaeology-fenton/summer_2011_final_small.pdf - showing how difficult it is to do the Gutman method of data remnance recovery
thanks for your input and clear guides, great references and many readers will follow your instructions.
Thanks. My pleasure.
I should clarify that both the Office Recovery and Cimaware programs have bulk file recovery too and may do a better job at recovering formatting. They are long established companies with many years experience and improving algorithms behind them and may be the best programs. However they are more expensive than Munsoft's. Users should try the demos first.
Munsoft's program occasionally appear as freeware for the day on the giveawayoftheday.com, if one is patient.
maybe they are corrupted, try another recovery tools maybe they can work better.
Repairing corrupted files in Excel
S2 Recovery Tools for Microsoft Excel
.NET4.0 version of the XLStylesTool is now available
Excel Regenerator... $99.99
Fix Excel File (Repair Corrupted Files, Fix Excel Errors, Recover Files, Fix Damaged Files, Corrupted Files, Fix to Open Excel) - Download Solutions
What is Protected View?
1. Open Excel
2. Click on File then Options.
3. Select Trust Center then Trust center settings.
4. Select Protected view.
5. Uncheck all the options under Protected View then click OK and restart Excel