1SAFECOPY(1) SAFECOPY SAFECOPY(1)
2
6 safecopy - rescue data from a source that causes IO errors
7
10 safecopy [OPTION]... SOURCE DEST
11
14 safecopy tries to get as much data from SOURCE as possible, even
15 resorting to device specific low level operations if applicable.
16 This is achieved by identifying problematic or damaged areas, skipping
18 over them and continuing reading afterwards. The corresponding area in
19 the destination file is either skipped (on initial creation that means
20 padded with zeros) or deliberately filled with a recognizable pattern
21 to later find affected files on a corrupted device.
22 Safecopy uses an incremental algorithm to identify the exact beginning
24 and end of bad areas, allowing the user to trade minimum accesses to
25 bad areas for thorough data resurrection.
26 Multiple passes over the same file are possible, to first retrieve as
28 much data from a device as possible with minimum harm, and then trying
29 to retrieve some of the remaining data with increasingly aggressive
30 read attempts.
31 For this to work, the source device or file has to be seekable. For
33 unseekable devices (like tapes) you can try to use an external script
34 to execute a controlled skip over the damaged part for you.
35 (For example by using "mt seek" and "mt tell" on an SCSI tape device)
37 See the "-S <seekscript>" parameter for details.
38 Performance and success of this tool depend extremely on the device
40 driver, firmware and underlying hardware.
41 Currently safecopy supports RAW access to CDROM drives to read data
43 directly of a CD, bypassing some driver dependant error correction.
44 This can speed up data retrieval from CDs and reduce system load during
45 recovery, as well as increase the success rate. Safecopy uses the disc
46 status syscall to determine sector size and addressing of CDs. This
47 fails on mixed-mode or multi-session CDs, since the sector layout can
48 change within the disk, but would still work on the the big majority of
49 disks. Other disks can still be recovered using normal high level data
50 access. Safecopy auto-detects the disk type involved during scan for
51 disk and block size.
52 Some CD/DVD drives are known to cause the ATAPI bus to crash on errors,
54 causing the device driver to freeze for times up to and beyond a minute
55 per error. Try to avoid using such drives for media recovery. Using
56 safecopys low level access features might help under some circum‐
57 stances.
58 Some drives can read bad media better than others. Be sure to attempt
60 data recovery of CDs and DVDs on several different drives and comput‐
61 ers. You can use safecopys incremental recovery feature to read previ‐
62 ously unreadable sectors only.
63
66 Data recovery from damaged media is a delicate task, in the worst case
67 its success or failure can safe or ruin whole companies and seal
68 affected peoples personal fate. It is paramount that any tools written
69 for that purpose are reliable and trustworthy.
70 A user needs to know what exactly the software is doing to his hardware
72 and data. The outcome of any operation needs to be both understandable
73 and predictable.
74 An "intelligent data resurrection wizard" with unknown complex internal
76 behaviour may be a nifty tool, but does not meet the above requirements
77 of predictable outcome, nor will the user know in advance what is done
78 to his data.
79 The operation sequence of safecopy has been kept relatively simple to
81 assure this predictability. Unfortunately feature additions have risen
82 the complexity and lead to undefined outcome in the past when include
83 and exclude lists had been mixed, especially when mixing different
84 block sizes. In the worst case this could have lead to overwritten data
85 in the destination file on a later incremental run with the mark (-M)
86 option.
87 From version 1.3 on, safecopy ships with a test suite that can be used
89 to verify safecopys behaviour in a set of test cases, simulating the
90 combination of bad blocks in input with different include and exclude
91 lists, both with and without marking. Releases are only made if safe‐
92 copy passes those test cases according to the specification.
93 This textual specification of behaviour of safecopy can be found in the
95 file specification.txt shipped with safecopy.
96
99 --stage1
100 Preset to rescue most of the data fast, using no retries and
101 avoiding bad areas.
102 Presets: -f 10% -r 10% -R 1 -Z 0 -L 2 -M BaDbLoCk -o stage1.bad‐
104 blocks
105 --stage2
107 Preset to rescue more data, using no retries but searching for
108 exact ends of bad areas.
109 Presets: -f 128* -r 1* -R 1 -Z 0 -L 2 -I stage1.badblocks -o
111 stage2.badblocks
112 --stage3
114 Preset to rescue everything that can be rescued using maximum
115 retries, head realignment tricks and low level access.
116 Presets: -f 1* -r 1* -R 4 -Z 1 -L 2 -I stage2.badblocks -o
118 stage3.badblocks
119 All stage presets can be overridden by individual options.
121 -b <size>
123 Blocksize for default read operations. Set this to the physical
124 sectorsize of your media.
125 Default: 1*
127 Hardware block size if reported by OS, otherwise 4096
128 -f <size>
130 Blocksize in bytes when skipping over badblocks. Higher set‐
131 tings put less strain on your hardware, but you might miss good
132 areas in between two bad ones.
133 Default: 16*
135 -r <size>
137 Resolution in bytes when searching for the exact beginning or
138 end of a bad area. If you read data directly from a device
139 there is no need to set this lower than the hardware blocksize.
140 On mounted filesystems however, read blocks and physical blocks
141 could be misaligned. Smaller values lead to very thorough
142 attempts to read data at the edge of damaged areas, but increase
143 the strain on the damaged media.
144 Default: 1*
146 -R <number>
148 At least that many read attempts are made on the first bad block
149 of a damaged area with minimum resolution. More retries can
150 sometimes recover a weak sector, but at the cost of additional
151 strain.
152 Default: 3
154 -Z <number>
156 On each error, force seek the read head from start to end of the
157 source device as often as specified. That takes time, creates
158 additional strain and might not be supported by all devices or
159 drivers.
160 Default: 1
162 -L <mode>
164 Use low level device calls as specified:
165 0 Do not use low level device calls
167 1 Attempt low level device calls for error recovery only
168 2 Always use low level device calls if available
169 Supported low level features in this version are:
171 SYSTEM DEVICE TYPE FEATURE
173 Linux cdrom/dvd bus/device reset
174 Linux cdrom read sector in raw mode
175 Linux floppy controller reset, twaddle
176 Default: 1
178 --sync Use synchronized read calls (disable driver buffering). Safe‐
180 copy will use O_DIRECT if supported by the OS and O_SYNC other‐
181 wise.
182 Default: Asynchronous read buffering by the OS is allowed
184 --forceopen
186 Keep trying to reopen the source after a read errer useful for
187 USB drives that go away temporarily.
188 Warning: This can cause safecopy to hang until aborted manually!
190 Default: Abort on fopen() error
192 -s <blocks>
194 Start position where to start reading. Will correspond to posi‐
195 tion 0 in the destination file.
196 Default: block 0
198 -l <blocks>
200 Maximum length of data to be read.
201 Default: Entire size of input file
203 -I <badblockfile>
205 Incremental mode. Assume the target file already exists and has
206 holes specified in the badblockfile. It will be attempted to
207 retrieve more data from the listed blocks or from beyond the
208 file size of the target file only.
209 Warning: Without this option, the destination file will be emp‐
211 tied prior to writing. Use -I /dev/null if you want to continue
212 a previous run of safecopy without a badblock list.
213 Implies: -c 0 if -c is not specified
215 Default: none ( /dev/null if -c is given )
217 -i <bytes>
219 Blocksize to interpret the badblockfile given with -I.
220 Default: Blocksize as specified by -b
222 -c <blocks>
224 Continue copying at this position. This allows continuing if
225 the output is a block device with a fixed size as opposed to a
226 growable file, where safecopy cannot determine how far it
227 already got. The blocksize used is the same as for the -I
228 option.
229 -c 0 will continue at the current destination size.
230 Implies: -I /dev/null if -I is not specified
232 Default: none ( 0 if -I is given )
234 -X <badblockfile>
236 Exclusion mode. If used together with -I, excluded blocks over‐
237 ride included blocks. Safecopy will not read or write any data
238 from areas covered by exclude blocks.
239 Default: none
241 -x <bytes>
243 Blocksize to interpret the badblockfile given with -X.
244 Default: Blocksize as specified by -b
246 -o <badblockfile>
248 Write a badblocks/e2fsck compatible bad block file.
249 Default: none
251 -S <seekscript>
253 Use external script for seeking in input file. (Might be useful
254 for tape devices and similar). Seekscript must be an executable
255 that takes the number of blocks to be skipped as argv1 (1-64)
256 the blocksize in bytes as argv2 and the current position (in
257 bytes) as argv3. Return value needs to be the number of blocks
258 successfully skipped, or 0 to indicate seek failure. The exter‐
259 nal seekscript will only be used if lseek() fails and we need to
260 skip over data.
261 Default: none
263 -M <string>
265 Mark unrecovered data with this string instead of skipping it.
266 This helps in later finding corrupted files on rescued file sys‐
267 tem images. The default is to zero unreadable data on creation
268 of output files, and leaving the data as it is on any later run.
269 Warning: When used in combination with incremental mode (-I)
271 this may overwrite data in any block that occurs in the -I file.
272 Blocks not in the -I file, or covered by the file specified with
273 -X are save from being overwritten.
274 Default: none
276 --debug <level>
278 Enable debug output. Level is a bit field, add values together
279 for more information:
280 program flow: 1
281 IO control: 2
282 badblock marking: 4
283 seeking: 8
284 incremental mode: 16
285 exclude mode: 32
286 or for all debug output: 255
287 Default: 0
289 -T <timingfile>
291 Write sector read timing information into this file for later
292 analysis.
293 Default: none
295 -h, --help
297 Show the program help text.
298
301 valid parameters for -f -r -b <size> options are:
302 <integer>
304 Amount in bytes - i.e. 1024
305 <percentage>%
307 Percentage of whole file/device size - e.g. 10%
308 <number>*
310 -b only, number times blocksize reported by OS
311 <number>*
313 -f and -r only, number times the value of -b
314
317 description of output symbols:
318 . Between 1 and 1024 blocks successfully read.
320 _ Read of block was incomplete. (possibly end of file) The block‐
322 size is now reduced to read the rest.
323 |/| Seek failed, source can only be read sequentially.
325 > Read failed, reducing blocksize to read partial data.
327 ! A low level error on read attempt of smallest allowed size leads
329 to a retry attempt.
330 [xx](+yy){
332 Current block and number of bytes continuously read successfully
333 up to this point.
334 X Read failed on a block with minimum blocksize and is skipped.
336 Unrecoverable error, destination file is padded with zeros.
337 Data is now skipped until end of the unreadable area is reached.
338 < Successful read after the end of a bad area causes backtracking
340 with smaller blocksizes to search for the first readable data.
341 }[xx](+yy)
343 current block and number of bytes of recent continuous unread‐
344 able data.
345
348 How do I...
349 - resurrect a file from a mounted but damaged media, that copy will
351 fail on:
352 safecopy /path/to/problemfile ~/saved-file
353 - create an filesystem image of a damaged disk/cdrom:
355 safecopy /dev/device ~/diskimage
356 - resurrect data as thoroughly as possible?
358 safecopy source dest -f 1* -R 8 -Z 2
360 (assuming logical misalignment of blocks to sectors)
361 safecopy source dest -f 1* -r 1 -R 8 -Z 2
363 - resurrect data as fast as possible, or
365 - resurrect data with low risk of damaging the media further:
367 (you can use even higher values for -f and -r)
368 safecopy source dest -f 10% -R 0 -Z 0
370 - resurrect some data fast, then read more data thoroughly later:
372 safecopy source dest -f 10% -R 0 -Z 0 -o badblockfile
374 safecopy source dest -f 1* -R 8 -Z 2 -I badblockfile
375 Alternate approach using the new preset features:
377 safecopy source dest --stage1
379 safecopy source dest --stage2
381 safecopy source dest --stage3
383 - utilize some friends CD-ROM drives to complete the data from my dam‐
385 aged CD:
386 safecopy /dev/mydrive imagefile <someoptions> -b <myblocksize>
387 -o myblockfile
388 safecopy /dev/otherdrive imagefile <someoptions> -b <otherblock‐
389 size> -I myblockfile -i <myblocksize> -o otherblockfile
390 safecopy /dev/anotherdrive imagefile <someoptions> -b <anoth‐
391 erblocksize> -I otherblockfile -i <otherblocksize>
392 - interrupt and later resume a data rescue operation:
394 safecopy source dest
395 <CTRL+C> (safecopy aborts)
396 safecopy source dest -I /dev/null
397 - interrupt and later resume a data rescue operation with correct bad‐
399 blocks output:
400 safecopy source dest <options> -o badblockfile
401 <CTRL+C> (safecopy aborts)
402 mv badblockfile savedbadblockfile
403 safecopy source dest -I /dev/null -o badblockfile
404 cat badblockfile >>savedbadblockfile
405 - interrupt and resume in incremental mode:
407 (this needs a bit of bash scripting to get the correct badblock
408 lists)
409 safecopy source dest <options> -o badblockfile1
410 safecopy source dest <options> -I badblockfile1 -o badblockfile2
411 <CTRL+C> (safecopy aborts)
412 latest=$( tail -n 1 badblockfile2 )
413 if [ -z $latest ]; then latest=-1; fi;
414 cat badblockfile1 | while read block; do
415 [ $block -gt $latest ] && echo $block >>badblockfile2;
416 done;
417 safecopy source dest <options> -I badblockfile2 -o badblockfile3
418 - find the corrupted files on a partially successful rescued file sys‐
420 tem:
421 safecopy /dev/filesystem image -M CoRrUpTeD
422 fsck image
423 mount -o loop image /mnt/mountpoint
424 grep -R /mnt/mountpoint "CoRrUpTeD"
425 (hint: this might not find all affected files if the unreadable
426 parts are smaller in size than your marker string)
427 - exclude the previously known badblocks list of a filesystem from
429 filesystem image creation:
430 dumpe2fs -b /dev/filesystem >badblocklist
431 safecopy /dev/filesystem image -X badblocklist -x <blocksize of
432 your fs>
433 - create an image of a device that starts at X and is Y in size:
435 safecopy /dev/filesystem -b <bsize> -s <X/bsize> -l <Y/bsize>
436 - combine two partial images of rescued data without access to the
438 actual (damaged) source data:
439 (This is a bit tricky. You need to get badblocks lists for both
440 files somehow to make safecopy know where the missing data is.
441 If you used the -M (mark) feature you might be able to automati‐
442 cally compute these, however this feature is not provided by
443 safecopy. Lets assume you have two badblocks files.
444 you have:
446 image1.dat
447 image1.badblocks (blocksize1)
448 image2.dat
449 image2.badblocks (blocksize2)
450 The file size of image1 needs to be greater or equal to that of
452 image2. (If not, swap them) )
453 cp image2.dat combined.dat
455 safecopy image1.dat combined.dat -I image2.badblocks -i block‐
456 size2 -X image1.badblocks -x blocksize1
457 (This gets you the combined data, but no output badblocklist.
458 The resulting badblocks list would be the badblocks that are
459 a: in both badblocks lists, or
460 b: in image1.badblocks and beyond the file size of image2 It
461 should be reasonably easy to solve this logic in a short shell
462 script. One day this might be shipped with safecopy, until then
463 consider this your chance to contribute to a random open source
464 project.)
465 - rescue data of a tape device:
467 If the tape device driver supports lseek(), treat it as any
468 file, otherwise utilize the "-S" option of safecopy with a to be
469 self-written script to skip over the bad blocks. (for example
470 using "mt seek") Make sure your tape device doesn't auto-rewind
471 on close. Send me feedback if you had any luck doing so, so I
472 can update this documentation.
473
476 Q: Why create this tool if there already is something like dd-res‐
477 cue and other tools for that purpose?
478 A: Because I didn't know of dd(-)rescue when I started, and I felt
480 like it. Also I think safecopy suits the needs of a user in data
481 loss peril better due to more readable output and more under‐
482 standable options than some of the other tools. (Then again I
483 am biased. Compare them yourself) Meanwhile safecopy supports
484 low level features other tools don't.
485 Q: What exactly does the -Z option do?
487 A: Remember back in MS-DOS times when a floppy would make a "neek
489 nark" sound 3 times every time when running into a read error?
490 This happened when the BIOS or DOS disk driver moved the IO head
491 to its boundaries to possibly correct small cylinder misalign‐
492 ment, before it tried again. Linux doesn't do that by default,
493 neither do common CDROM drives or drivers. Nevertheless forcing
494 this behaviour can increase your chance of reading bad sectors
495 from a CD __BIG__ time. (Unlike floppies where it usually has
496 little effect)
497 Q: Whats my best chance to resurrect a CD that has become unread‐
499 able?
500 A: Try making a backup image on many different computers and
502 drives. The abilities to read from bad media vary extremely. I
503 have a 6 year old Lite On CDRW drive, that even reads deeply and
504 purposely scratched CDs (as in with my key, to make it unread‐
505 able) flawlessly. A CDRW drive of the same age at work doesn't
506 read any data from that part of the CD at all, while most DVD
507 and combo drives have bad blocks every couple hundred bytes.
508 Make full use of safecopys RAW access features if applicable.
509 (-L 2 option)
510 As a general guideline: -CDRW drives usually do better than
512 read-only CD drives.
513 -CD only drives sometimes do better on CDs than DVD drives.
514 -PC drives are sometimes better than laptop ones.
515 -A drive with a clean lens does better than a dirtball.
516 -Cleaning up CDs helps.
517 -Unless you use chemicals.
518 -Using sticky tape on a CD will rip of the reflective layer per‐
519 manently rendering the disk unreadable.
520 Q: Whats my best chance to resurrect a floppy that became unread‐
522 able?
523 A: Again try different floppy drives. Keep in mind that it might be
525 easier to further damage data on a bad floppy than on a CD.
526 (Don't overdo read attempts)
527 Q: What about BlueRay/HDDVD disks?
529 A: Hell if I knew, but generally they should be similar to DVDs.
531 It probably depends how the drives firmware acts up.
532 Q: My hard drive suddenly has many bad sectors, what should I do?
534 A: Speed is an essential factor when rescuing data from a bad hard
536 drive. Accesses to bad areas or even just time running can fur‐
537 ther damage the drive and make formerly readable areas unread‐
538 able, be it due to temperature rise, damaged heads scratching
539 still good parts of the surface, bearings degrading due to
540 vibration, etc. Its advisable to shut the system down and
541 remove the hard drive from the computer as soon as errors occur
542 and as fast as possible without causing further damage.
543 (Don't pull the plug! Press reset to force reboot and then power
545 down via power button/ACPI)
546 Set up a rescue system with enough disk space to store all the
548 data from the damaged drive (and possibly multiple copies of
549 it). If you have an external hard drive case that connects via
550 USB SATA or SCSI, allowing a hot plug of the drive into a run‐
551 ning system, use it. This allows you to prepare everything
552 without the need for the drive to power up and possibly BIOS or
553 operating system involuntarily accessing it. You also get eas‐
554 ier access to the drive to check temperature or noise during
555 operation.
556 When you rescue data, rescue good data first before attempting
558 to access bad sectors. Safecopy allows you to skip known problem
559 sectors using a badblock exclude file (-X) which you might be
560 able to retrieve from system logs or from the drive internal
561 logs, via smartmontools or similar software. Be aware that you
562 might possibly need to convert physical sector numbers into log‐
563 ical block numbers depending on your source.
564 Also you should tell safecopy to jump out of any problematic
566 areas ASAP and continue somewhere else. Parameters "-f 10% -r
567 10% -R 0 -Z 0" would do the trick by making safecopy skip 10% of
568 the device content and continue there without backtracking. You
569 can always attempt to get the data in between later, first get
570 the supposedly good data on the rest of the drive. Depending on
571 the method of data recovery you plan on using, it may make sense
572 to mark the bad data with the "-M" option. This allows you to
573 later find files affected by data corruption more easily. Use
574 the "-o" option to make safecopy write a badblock list with all
575 blocks skipped or unreadable.
576 When safecopy is done with this first run, you can attempt a
578 second go trying to get more data. Using smaller values for "-f"
579 and allowing safecopy to backtrack for the end of the affected
580 area "-r 1*". Be sure to use incremental mode "-I" to only read
581 the blocks skipped in the first run.
582 It may make sense to let the drive cool down between runs. Once
584 you got all the data from the "good" areas of the drive you can
585 risk more "thorough" access to it. Increase the numbers of
586 retries "-R" in case of bad blocks, maybe together with a head
587 realignment "-Z 1". "-f 1*" would make safecopy try to read on
588 every single block, not skipping over bad areas at all.
589 If your drive stops responding, power it down, let it cool down
591 for a while, then try again.
592 (I heard from people who brought dead drives back to live for a
594 short time by cooling them to low temperatures with ice-packs.)
595 !!! If the data is really important, go to a professional data
597 recovery specialist right away, before doing further damage to
598 the drive.
599
602 safecopy returns 0 (zero) if there were no unrecoverable errors.
603 safecopy returns 1 if some data could not be recovered.
604 safecopy returns 2 in case the copying was aborted due to error or sig‐
605 nal.
606
609 safecopy and its manpage have been designed and written by CorvusCorax.
610
613 Please use the project page on sourceforge
614 <http://www.sf.net/projects/safecopy> to get in contact with project
615 development if you encounter bugs or want to contribute to safecopy.
616
619 Copyright © 2009 CorvusCorax
620 This is free software. You may redistribute copies of it under the
621 terms of the GNU General Public License version 2 or above.
622 <http://www.gnu.org/licenses/gpl.html>. There is NO WARRANTY, to the
623 extent permitted by law.
624
627 Programs with a similar scope are among others
628 ddrescue(1), dd-rescue(1), ...
629 2012-03-10 SAFECOPY(1)