Will there be Physical device objects (PDOs) for SCSI disks connected to a SCSI HBA?

Posted on 2012-09-19
Last Modified: 2012-09-22
Generally there are bus drivers for various kinds of buses. One such example is a PCI bus driver. The bus driver creates a PDO (Physical device  objects) for every device on that bus.
Hence if i have a SAS Host based adapter (storage controller ) on the PCI bus, there will be corresponding PDO for that as well.

Now when there are SAS disks connected to the HBA, typically the disks will be on a SCSI bus. My question is whether there will be a PDO for each of these SAS disks as well? If yes, who will create those PDO?  If not, why not?
Question by:raj_ksrt
    LVL 77

    Expert Comment

    by:David Johnson, CD, MVP
    AFAIK, Yes there will be for each physical disk. If you use RAID then the output of the raid will be presented to the o/s as the physical disk.

    Author Comment

    which bus driver will be  responsible for creating the PDOs for scsi disks? I dont think it is the PCI bus driver.
    LVL 12

    Accepted Solution

    There shouldn't be any difference between PATA, SATA, SCSI and SAS. In each of these there is a controller that sits on the bus and that controls the underlying devices.

    As you can see from:-

    typically for each of these controller types there will be a port driver that provides the window from the OS to the underlying devices. It is this port driver that enumerates the underlying storage devices and builds the PDOs.

    Note that RAID is a little more complex. The RAID controller usually presents itself a SCSI disk controller but the OS never sees the physical disks. Instead the RAID controller presents each RAID array as a physical disk and a PDO is built for each RAID array. Disk Manager sees the RAID array as a physical disk and allows you to format it as such.

    There is a nice presentation on this here:-

    but note its from a conference so isn't definitive.

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