On Thu, 4 Apr 2002, at 1:17pm, Derek D. Martin wrote:
> How is the SCSI card going to access the information on the IDE (i.e.
> not connected to it) disks?
It isn't. The OP wants to turn his Linux box into a SCSI RAID controller.
Consider those SCSI-to-SCSI RAID boxes from Winchester Systems that MCLX
was using. You have one or more SCSI buses in the drive array. Those buses
connect to the RAID controller in the box, which is nothing more than a
specialized computer. The other side of the RAID controller is simply
another set of SCSI interfaces. The program in the RAID controller makes
the magic happen.
There is no reason, from a technology standpoint, that one could not do
the same with commodity PC hardware. You start with IDE disks attached to
a system, as normal. You use "software" RAID to aggregate the disks
together into one big "virtual block device" (with the "md" driver).
Now put a SCSI host adapter into the same box. Put the HA into target
mode. Write a special program which presents block devices in the Linux
host as SCSI LUNs on the HA. Other devices on the SCSI bus can now access
the Linux box as if it were a disk drive.
[IDE_HDD] [IDE_HDD]
| | <---- IDE buses
[Linux_IDE_driver]
| | <---- kernel block device layer
[Linux_md_subsystem]
| <---- kernel block device layer
[SCSI_block_device_translation_emulation_thingy]
| <---- kernel SCSI mid-level layer
[SCSI_host_adapter_in_target_mode]
| <---- SCSI bus
[SCSI_host]
> Can SCSI controllers talk to SCSI devices attached to DIFFERENT SCSI
> controllers?
No. (Well, I suppose you could submit requests on bus via proxy on
another, but that isn't really the same thing, and you would run out of SCSI
IDs rather quickly.)
--
Ben Scott <[EMAIL PROTECTED]>
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