Re: Accessing discs connected to H/W RAID controller over SG interface

["Martin K. Petersen" <martin.petersen@oracle.com>]

Tom,

> The RAID controller from Areca is configured with 2-off RAID volumes
> and has 4-off 6TB discs attached to it.  I would like to be able to
> access the 4 discs individually, e.g. to be able to dd them to
> /dev/null to check on their performances.

It really depends on the RAID controller whether it is possible to
directly access physical disks. Most controllers disallow accessing any
drives that are part of a logical RAID volume.

Those controllers that expose physical disks will typically only present
them as generic SCSI devices for purposes of health monitoring and drive
firmware updates. The controller firmware will often only allow a few
carefully curated SCSI commands to be passed through to the physical
drive.

The reason you can query the drives through smartctl is that the latter
has special code which knows how to address individual drives behind an
areca interface. But querying SMART data is not the same as being able
to send or receive arbitrary SCSI commands.

-- 
Martin K. Petersen	Oracle Linux Engineering