pakr-rawata 1.0.0

Raw access to hard disks - read using READ_DMA_EXT (0x25), write using WRITE_DMA_EXT (0x35) and identify using IDENTIFY_DEVICE (0xEC). On Linux uses SG subsystem, on FreeBSD uses CAM subsystem. Warning, it bypasses all OS security checks and all software caches. You can kill data on your HDD in a blink of an eye.
Documentation

Raw access to hard disks for Linux and FreeBSD. For technical information refer to ATA/ATAPI Command Set guide.

Warning

it bypasses all OS security checks and all software caches. You can kill the data on your HDD in a blink of an eye. The only protection is that it requires administrative privilege to run.

Supported operations

  • read sectors using READ_DMA_EXT (ATA cmd 0x25, documentation chapter 7.21),
  • write sectors using WRITE_DMA_EXT (ATA cmd 0x35, documentation chapter 7.57)
  • identify drive using IDENTIFY_DEVICE (ATA cmd 0xEC, documentation chapter 7.13, including a detailed description of returned structure).

On Linux uses SG subsystem, on FreeBSD uses CAM subsystem.

Note

In theory, a single ATA DMA transfer is limited to 65536 sectors (32MiB for 512B sectors). Sector count is 16 bit and a full 65536 sector transfer is indicated by a sector count of 0x0000).

In practice operating system enforces much lower limit, in the range of a few hundred kilobytes.

On FreeBSD I managed to achieve stable transfers of 8MB at a time by re-compiling kernel with custom configuration:

include GENERIC

ident           BIGDMA

options         DFLTPHYS=(16U*1024*1024)
options         MAXPHYS=(32U*1024*1024)

On Linux I didn't find any accessible tunable to bump-up the maximal DMA transfer size, neither compile-time nor run-time.

TODO

  • support sector sizes different than 512 bytes