paulf@inmos.co.uk (Paul Fellows) (12/18/90)
In Article 1335 Bryan Hennessy writes : > I am investigating the viability of a RAID(Redundant Array of Inexpensive Disks) > system. This would require the connection of about 20 disks. However only a few > SCSI addresses are available to connect the system. To get around this problem > I was wondering if it is possible to buy a SCSI device that contains several > other SCSI chips and can multiplex one SCSI address onto these SCSI chips > (using the LUN) effectively extending the number of SCSI addresses available. > > Any help on this matter would be much appreciated. > > Bryan Hennessy, bhnnessy@cs.tcd.ie > University of Dublin, Trinity College, > IRELAND. We use 2 of our credit card sized SCSI Transputer modules (Tram's) back to back to do what you describe. The 2 Trams talk to each other by transputer links (2 twisted pairs) at 1.5 Mbytes per second. Each module has 4 such links which work automonously (DMA) with the onboard 16 bit 20 Mhz Transputer. The SCSI bus interface is implemented by an NCR 53c94 Enhanced SCSI Processor. A comprehensive software package that supports both initiator and target modes is provided inclusive. The modules can be mounted on a PC or VME mother board (IMS B008 or IMS B014). In the diagram below, a single target appears to the host as a target which manages 7 LUNS's. If three SCSI Trams were used, then the target could manage 8 Luns and also implement redunancy (Disk Mirroring or Striped ECC). Using 4 Disks, 4 SCSI Trams and a Graphics Tram (IMS B419), we successfully transferred a sequence images from the 4 disks in parallel into the graphics display memory of of the B419 at a SUSTAINED 5 Mbytes per second. (Video animation rates). |=========| | Host | |---------| Links |---------| | Computer|===========|IMS B422 |---------|IMS B422 |=============| | | SCSI | SCSI |---------| SCSI | SCSI | | | Bus | TRAM |---------| TRAM | Bus | | |===========| Target |---------|Initiator|======| | |=========| |---------| |---------| | | | | |======|=| | |Lun 0 | | | | | |======|=| | | | |======|=| | |Lun 1 | | | | | |======|=| | | | |======|=| | |Lun 2 | | | | | |======|=| | | | |======|=| | |Lun 3 | | | | | |======|=| | | | |======|=| | |Lun 4 | | | | | |======|=| | | | |======|=| | |Lun 5 | | | | | |======|=| | | | |======|=| | |Lun 6 | | | | | |======|========| Paul Fellows, INMOS Limited | mail(uk): paulf@inmos.co.uk or ukc!inmos!paulf Bristol, England | (us): uunet!inmos.com!paulf +44 454 616616 ex 618 | Internet: paulf@inmos.com