freebsd man page for recoverdisk

RECOVERDISK(1)						    BSD General Commands Manual 					    RECOVERDISK(1)

NAME
     recoverdisk -- recover data from hard disk or optical media

SYNOPSIS
     recoverdisk [-b bigsize] [-r readlist] [-s interval] [-w writelist] source [destination]

DESCRIPTION
     The recoverdisk utility reads data from the source file until all blocks could be successfully read.  If destination was specified all data
     is being written to that file.  It starts reading in multiples of the sector size.  Whenever a block fails, it is put to the end of the work-
     ing queue and will be read again, possibly with a smaller read size.

     By default it uses block sizes of roughly 1 MB, 32kB, and the native sector size (usually 512 bytes).  These figures are adjusted slightly,
     for devices whose sectorsize is not a power of 2, e.g., audio CDs with a sector size of 2352 bytes.

     The options are as follows:

     -b bigsize
	     The size of reads attempted first.  The middle pass is roughly the logarithmic average of the bigsize and the sectorsize.

     -r readlist
	     Read the list of blocks and block sizes to read from the specified file.

     -s interval
	     How often we should update the writelist file while things go OK.	The default is 60 and the unit is "progress messages" so if things
	     go well, this is the same as once per minute.

     -w writelist
	     Write the list of remaining blocks to read to the specified file if recoverdisk is aborted via SIGINT.

     The -r and -w options can be specified together.  Especially, they can point to the same file, which will be updated on abort.

OUTPUT
     The recoverdisk utility prints several columns, detailing the progress

     start	Starting offset of the current block.

     size	Read size of the current block.

     len	Length of the current block.

     state	Is increased for every failed read.

     done	Number of bytes already read.

     remaining	Number of bytes remaining.

     % done	Percent complete.

EXAMPLES
     # recover data from failing hard drive ada3
     recoverdisk /dev/ada3 /data/disk.img

     # clone a hard disk
     recoverdisk /dev/ada3 /dev/ada4

     # read an ISO image from a CD-ROM
     recoverdisk /dev/cd0 /data/cd.iso

     # continue reading from a broken CD and update the existing worklist
     recoverdisk -r worklist -w worklist /dev/cd0 /data/cd.iso

     # recover a single file from the unreadable media
     recoverdisk /cdrom/file.avi file.avi

     # If the disk hangs the system on read-errors try:
     recoverdisk -b 0 /dev/ada3 /somewhere

SEE ALSO
     dd(1), ada(4), cam(4), cd(4), da(4)

HISTORY
     The recoverdisk utility first appeared in FreeBSD 7.0.

AUTHORS
     The original implementation was done by Poul-Henning Kamp <phk@FreeBSD.org> with minor improvements from Ulrich Sporlein <uqs@FreeBSD.org>.

     This manual page was written by Ulrich Sporlein.

BUGS
     Reading from media where the sectorsize is not a power of 2 will make all 1 MB reads fail.  This is due to the DMA reads being split up into
     blocks of at most 128kB.  These reads then fail if the sectorsize is not a divisor of 128kB.  When reading a full raw audio CD, this leads to
     roughly 700 error messages flying by.  This is harmless and can be avoided by setting -b to no more than 128kB.

     recoverdisk needs to know about read errors as fast as possible, i.e. retries by lower layers will usually slow down the operation.  When
     using cam(4) attached drives, you may want to set kern.cam.XX.retry_count to zero, e.g.:

     # sysctl kern.cam.ada.retry_count=0
     # sysctl kern.cam.cd.retry_count=0
     # sysctl kern.cam.da.retry_count=0

BSD
								  October 1, 2013							       BSD