recoverdisk man page on FreeBSD

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

     recoverdisk — recover data from hard disk or optical media

     recoverdisk [-b bigsize] [-r rlist] [-s snapshot] [-w wlist] special

     The recoverdisk utility reads data from the special file until all blocks
     could be successfully read.  It starts reading in multiples of the sector
     size.  Whenever a block fails, it is put to the end of the working 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 sec‐
     tor 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 sec‐
     tor 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 rlist
	     Read the list of blocks and block sizes to read from the speci‐
	     fied file.

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

     -w wlist
	     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.

     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.

     # recover data from failing hard drive ad3
     touch /data/lots_of_space
     recoverdisk /dev/ad3 /data/lots_of_space

     # clone a hard disk
     recoverdisk /dev/ad3 /dev/ad4

     # read an ISO image from a CD-ROM
     touch /data/cd.iso; recoverdisk /dev/acd0 /data/cd.iso

     # continue reading from a broken CD and update the existing worklist
     recoverdisk -r worklist -w worklist /dev/acd0 /data/cd.iso

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

     # If the disk hangs the system on read-errors try:
     recoverdisk -b 0 /dev/ad3 /somewhere


     The recoverdisk utility first appeared in FreeBSD 7.0.

     The original implementation was done by Poul-Henning Kamp
     ⟨⟩ with minor improvements from Ulrich Spörlein

     This manual page was written by Ulrich Spörlein.

     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 divi‐
     sor of 128kB.  When reading a full raw audio CD, this leads to roughly
     700 error messages flying by.  This is harmless.

BSD				  May 6, 2006				   BSD

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