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Question about SCSI tape transfers - SCO

Occasionally, on my OSR505 system, I have to copy the contents of a Travan5 tape to a Travan4 tape. I have both tape drives connected to a common SCSI HA and each drive is set to an unique SCSI ID and the transfer is performed using the dd command, such as: dd if=/dev/rStp0 of=/dev/rStp1 There are security implications for me if the bits touch, say, the hard drive or are cached or buffered somewhere on the system outside of the drive-HA-drive path. Question: as the bits flow from one tape cartridge to the other, do they ever "touch" any component ...

  1. #1

    Default Question about SCSI tape transfers

    Occasionally, on my OSR505 system, I have to copy the
    contents of a Travan5 tape to a Travan4 tape.

    I have both tape drives connected to a common SCSI HA
    and each drive is set to an unique SCSI ID and the
    transfer is performed using the dd command, such as:

    dd if=/dev/rStp0 of=/dev/rStp1

    There are security implications for me if the bits
    touch, say, the hard drive or are cached or buffered
    somewhere on the system outside of the drive-HA-drive
    path.

    Question: as the bits flow from one tape cartridge
    to the other, do they ever "touch" any component of
    the system other than the HA and tape drives?

    TIA.

    DDinAZ
    Dave Dickerson Guest

  2. #2

    Default Re: Question about SCSI tape transfers

    On Fri, 11 Jul 2003 23:08:08 GMT, Bela Lubkin <belalsco.com> wrote:
    >Dave erson wrote:
    >
    >> Occasionally, on my OSR505 system, I have to copy the
    >> contents of a Travan5 tape to a Travan4 tape.
    >>
    >> I have both tape drives connected to a common SCSI HA
    >> and each drive is set to an unique SCSI ID and the
    >> transfer is performed using the dd command, such as:
    >>
    >> dd if=/dev/rStp0 of=/dev/rStp1
    >>
    >> There are security implications for me if the bits
    >> touch, say, the hard drive or are cached or buffered
    >> somewhere on the system outside of the drive-HA-drive
    >> path.
    >>
    >> Question: as the bits flow from one tape cartridge
    >> to the other, do they ever "touch" any component of
    >> the system other than the HA and tape drives?
    >
    >The data is buffered in main system memory -- OpenServer does not
    >orchestrate direct SCSI target-to-target transfers. Also, since `dd` is
    >a user-level process, its memory image _could_ get written to swap space
    >if the system was busy enough to be swapping during the transfer. This
    >is altogether unlikely on modern systems, but you should be aware of the
    >possibility.
    >
    >To work around the swap issue, you could write your own data transfer
    >program and use plock(S) to force your process not to be swapped. The
    >process must run as root:
    >
    > #include <sys/lock.h>
    >
    > ...
    > if (plock(DATLOCK) < 0) {
    > perror("Cannot lock self in core (plock(DATLOCK))");
    > exit(1);
    > }
    >
    >Note that this is cleared by both fork() and exec(): you cannot use it
    >to lock down `dd`, you have to write your own data transfer program. Of
    >course it's a trivial program, in this case...
    >
    >>Bela<
    Bela, your reply is very much appreciated.

    Unfortunatly, writing even a trivial program is not an
    option for my situation but it is very helpful to know
    that data is touching the system during the transfer.

    Thank you for the technical insight.

    DDinAZ
    Dave Dickerson Guest

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