Re: Need Clarification regarding SCSI, HostRAID and RAID

"XxLicherxX" <goldhors64@xxxxxxx>,
In a message on 24 Jan 2006 06:04:14 -0800, wrote :

"> Hello everyone,
">
"> On my server, I have the following listed in Device Manager:
">
"> "Adaptec SCSI embedded HostRAID Controller"
">
"> Initially I believed that the server had a normal SCSI controller and
"> connected a normal SCSI tape library to it, however I have been
"> experiencing problems backing up to this device. Am I wrong in thinking
"> that I can do this?
">
"> What is the difference between a HostRAID Controller and a RAID
"> controller? Forgive my ignorance, but I thought RAID was only something
"> you used with hard drives.

A 'HostRAID Controller' and a 'RAID controller' are probably much the
same thing. You have some flavor of Adaptec SCSI RAID Controller on
your motherboard ('embedded'), probably an i2o type of thingy. There is
also the notion of a non-host SCSI RAID Controller -- this is a SCSI
*device* that is a RAID controller for a separate SCSI (or IDE) bus(s).
An older flavor of this is the DEC HSZ70 system. The 'host' computer
(eg AlphaServer) would have a plain SCSI controller and the HSZ70 would
show up as a single disk (with possibly several LUNs, one for each RAID
set, plus one for the controller itself). These are not too common
these days. A HostRAID controller is a RAID controller that connects a
bunch of disks directly to a host (motherboard), commonly via the PCI
bus, either in a card slot or on the motherboard itself.

Yes, RAID only makes sense with hard drives. *Some* RAID Controllers
will interface with non disks (eg tape drives, CD-ROM/CD-R drives, etc.)
and some won't. Some require you to use a different driver (eg a driver
that treats the RAID Controller as a plain SCSI Controller). Some will
let you talk to them with two drivers and do RAID with disks and
non-RAID access to non-disks. Some might need two drivers to do that.
It all depends on how the controller works and how it is 'connected' to
the system bus.

">
"> Thanks
">
">

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