Testing CAM wrapper for ata(4) controller drivers

Alexander Motin mav at FreeBSD.org
Sun Dec 6 17:33:22 UTC 2009

Alexander Best wrote:
> i've stumbled over a problem with ATA_CAM. when i accessing my dvd-drive i'm
> not able to access any other cam members (ada* e.g.).
> when i issue the following command:
> `cdrecord dev=2,1,0 blank=all'
> binaries such as ls, top or vmstat simply stall until cdrecord finishes.
> this is the output of `camcontrol devlist -v':
> scbus2 on ata2 bus 0:
> <HDS722516VLAT80 V34OA63A>         at scbus2 target 0 lun 0 (ada0,pass0)
> <HL-DT-ST DVDRAM GSA-H10N JL12>    at scbus2 target 1 lun 0 (pass1,cd0)
> <>                                 at scbus2 target -1 lun -1 ()

It was always bad idea to put CD and disk, which need to be used
simultaneously, to the same PATA channel. PATA channel can execute only
one command at a time, without using special technique, named overlap
(part of TCQ), which is usually not supported by devices. When your
blank command occupied CD, disk became inaccessible, until it complete.

Alexander Motin

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