2950 RAID controllers lack SCSI-passthrough setting

James Ralston qralston+ml.dell-poweredge at andrew.cmu.edu
Thu Feb 8 14:48:17 CST 2007

With PowerEdge 2650 and 2850 servers, the hardware RAID (PERC)
controller could be configured to SCSI "passthrough" mode in the BIOS.
In passthrough mode, the system acted like no PERC card was installed;
the OS saw the individual disks.

Unfortunately, the PERC controllers in PowerEdge 2950 servers do not
seem to offer this functionality: if you disable the PERC controller,
you cannot see the disks.

This is a major setback for us, because it means that we cannot have a
single hardware pool for both our Windows servers (which cannot do
software RAID and thus require the PERC controllers) and our Linux
servers (for which we have found software RAID far more manageable).

This might seem like a minor issue, but it's not: having to keep track
of "Linux" 2950s versus "Windows" 2950s is a major headache.  The
alternative is having to swap PERC cards versus SCSI cards around
whenever we want to deploy a server, which is also a headache,
particular if the deployment is an emergency (e.g., caused by a need
to replace failed hardware).

(Creating single-drive RAID 0 containers isn't an acceptable
workaround, as we want to avoid requiring the OS to drive the hardware
RAID card entirely.)

Is there any chance of bringing back the "passthrough" functionality?

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