--- /dev/null
+$Id$
+
+
+badblock-guess: Quickly recover most of the data from a damaged disk
+
+
+Purpose
+-------
+
+badblock-guess will try to find all readable sectors of the disk in minimal
+time. It is similiar to:
+ dd if=<src_dev> of=<dst_dev> bs=512 conv=noerror,sync
+
+but dd(1) solution can last for many weeks/months on heavily corrupted disk
+media as each bad sector attempted to be read costs about 5secs (your disk
+bad-blocks performance may significantly vary). badblock-guess tries to first
+find and recover most of the data from healthy zones of the disk and later it
+will start trying to recover smaller bits of information spread between/around
+badblock zones - the principle of its operation is the fact that badblocks
+usually occur in chunks. If you don't user-terminate badblock-guess and leave
+it to finish completely itself, its execution time should be approx. the same
+as for dd(1). You may also use it to guess the remaining execution time as
+during its later execution phases it will be showing the remaining number of
+sectors ("TODO=x") while most of them are probably badblocks in this phase of
+execution.
+
+This program will not recover data of any sector with failing read command.
+If dd(1) command above finishes for you in a reasonable time, you don't need
+this program. No special read methods are used. No vendor-specific dependencies
+exist. No IDE, SCSI or any other specific device is required.
+
+
+License
+-------
+
+GNU GENERAL PUBLIC LICENSE, Version 2, June 1991.
+
+See the file COPYING for its details. It is also available at:
+ http://www.gnu.org/licenses/gpl.txt
+
+
+Usage
+-----
+
+Syntax: badblock-guess <src_dev> [<dst_dev (OVERWRITTEN & DESTROYED!!!)>]
+
+Possible device cases (watch out for <src_dev> vs. <dst_dev> differences!):
+
+ No <dst_dev> is specified: Just the <src_dev> is scanned for errors and
+ the detected badblocks list is output.
+
+ <src_dev> is a harddrive (/dev/hdc): Other harddrive of equal or higher
+ capacity is recommended
+
+ <src_dev> is a partition (/dev/hdc1): Partition on any other physical
+ drive in the system with the exactly same partition size is
+ recommended
+
+ <dst_dev> is a file: File must exist but it will be enlarged when
+ needed. Commands:
+ rm -f /tmp/hdc1.img; touch /tmp/hdc1.img
+ are recommended to specify file "/tmp/hdc1.img" for <dst_dev>
+
+All the numbers are always expressed as sector (that means 512 bytes)
+number/count!
+
+Never terminate badblock-guess by CTRL-C or kill(1) if you want to utilize its
+results - always use 'f' followed by ENTER ('f' for 'finish'). You may not see
+'f' while typing it - type it blindly (without quotes - just the one letter!).
+During finishing the program will produce the badblocks list output to its
+stdout while it will be clearing the 'bad' or 'not-yet-done' zones of the
+target disk (if any specified).
+
+TODO: Resuming of the operation from the badblocks list to continue the
+ scanning is not yet implemented.
+
+
+hdparm
+------
+
+Although not required it is strongly recommended to turn of drive readahead
+during severe disk failure recoveries. You can use
+
+ /sbin/hdparm -A0a0 /dev/hdX (or /dev/sdX etc.)
+
+for your drive to do it. You may need to install some extra package with
+hdparm(8) for your Linux distribution.
+
+Be aware that the disk performance will be critically hit - you may expect read
+performance about 90KB/s (approx. 7.5GB/24hours if no badblocks read retrying
+is needed). YMMV.
+
+
+Compilation
+-----------
+
+Type:
+ make
+
+And you should have now the binary file "badblock-guess" compiled out.
+You may need to install the following packages of your Linux distribution:
+ e2fsprogs, e2fsprogs-devel
+ glib, glib-devel (this is NOT glibc!)
+ other standard C compilation tools and libraries...
+
+Compiled out binary is fully statically linked, you can bring it with you on
+the floppy everywhere (running Linux is still required, of course!).
+
+
+Operation description
+---------------------
+
+During its run it will update its progress line. All the numbers are always
+expressed as sector (that means 512 bytes) number/count.
+
+ @342342/819223,TODO=8192,bad=0,largest=8192,hunks=1
+ ^A ^B ^C ^D ^E ^F
+
+A=currently reding sector 342342 ...
+B=... out of total sector 819223 of the disk (or partition)
+C=8192 secters weren't yet attempted to be read
+D=0 sectors were found with proof of read failure
+E=currently read hunk of 8192 sectors
+ =also there is a maximum size of hunk 8192 sectors
+F=total remaining hunks to be processed
+
+Initially there is just one hunk (0-media_size) to be read. When no errors on
+the disk are found, this one hunk is finished and no output (bad sectors list)
+is generated.
+
+When we find bad a sector, we divide our todo-listed hunks by the schema:
+
+> successfuly read 10 ->[1 bad]<todo 1><todo 2><todo 4><todo 9><todo 19>|end
+
+We always read the biggest hunk "todo", "todo" hunks of the size are read in
+backwards order (to approach the found bad blocks from the other side).
+
+In this case the program would start with the status line (*):
+
+@27/46,TODO=35,bad=1,largest=19,hunks=5
+ ^A ^B ^C ^D ^E ^F
+
+A=we start reading the first sector of the largest hunk <todo 19> (10+1+1+2+4+9)
+B=total number of sectors on the disk (10+1+1+2+4+9+19)
+C=still have to read all <todo> hunks (1+2+4+9+19)
+D=we found just one confirmed bad sector <bad 1> (1)
+E=the largest hunk "todo" on the disk is <todo 19> (19)
+F=total number of the remaining "todo" hunks <t1><t2><t4><t9><t19> (1+1+1+1+1)
+
+If you terminate badblock-guess run (by 'f' key, see above!), you can be sure
+that you will loose the data of at most <largest> sectors after any bad sector
+found. But you still can loose <TODO> sectors of data.
+
+(*) The status line is printed once per a second and thus in real you can't
+ predict the exact states of the progress status line, of course.
+
+
+Output badblock list format
+---------------------------
+
+Output badblock list has form
+
+first_sector-behind_last_sector <tab> ;<comments>
+
+"behind_last_sector" is last_bad_sector+1. Thus single bad sector would be:
+ 5678-5679
+
+The following three types of output lines can occur. The first one is just
+a shortcut for the second+third - such output is chosen when TODO blocks are
+consequently following BAD blocks.
+
+1000-9192 ;BAD=100, TODO(@1100-@9192)=8092
+1000-1100 ;BAD=100
+1100-9192 ;TODO=8092
git://git.jankratochvil.net / badblock-guess.git / blobdiff