mkarcher wrote on 2023-11-06, 20:39:This sounds like you are confusing SCA (single connector attachment) with SCAM (SCSI configured AutoMagically). […]
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ElectroSoldier wrote on 2023-11-06, 18:31:
SCA is designed to get its ID from the controller. You dont have to set anything on the drive if youre using it properly, as designed.
This sounds like you are confusing SCA (single connector attachment) with SCAM (SCSI configured AutoMagically).
- SCA uses an 80-pin connector, which has 4 contacts used to configure a "hard" SCSI ID in the range 0..15. The "hard" SCSI ID configured via the SCA connection is used the same way as the jumpered SCSI ID is used on drives without an SCA connector. The purpose of SCA is to make drive replacement easier in systems designed for easily swappable drives. As the hard ID is configured using contacts on the SCA connectors, a replacement drive is automatically set to the same hard SCSI ID as the had that was replaced. Furthermore, there is no longer a separate power connector, and the drive replacement procedure is reduced to "unlock old drive", "pull old drive", "push in new drive" and "lock new drive".
- SCAM is a protocol that can assign a "soft" SCSI ID to any SCAM-compliant SCSI device on the SCSI bus, which will be used instead of the "hard" SCSI ID. This protocol works with any kind of connector, even with 50-pin narrow single-ended drives. The purpose of SCAM is to make SCSI configuration easier without requiring any kind of physical changes to the present SCSI system.
As SCAM can be implemented in any physical configuration of the parallel SCSI bus, SCAM can be used in systems with SCA drive connectors, but this is completely optional. If SCAM is used in an SCA system, the IDs set via SCA indeed don't matter, but you can't assume all SCA systems are using SCAM. I would expect the opposite: SCA really shines for hot plug bays in storage-server devices (including SANs), and these kind of systems want a fixed relation between a physical slot and an SCSI ID, because this allows the management software to display what physical slot contains the broken drive. If all drives were configured to the same hard ID and the soft IDs to be used were assigned using SCAM, the management software would have no idea what drive is in what physical slot.
No im not confusing anything but the way Im explainging it might well be confusing for some who dont know.
I have an SCA backplane, its a multiple drive box whos drives go into caddies.
The drives themselves are SCA.
The rear of the backplane has 2 68 pin connectors, one goes to the controller card, the other to another SCSI device or terminator.
There are 3 molex connectors for drive power
There are 5 dip switches for SCSI ID selection of each device.
Those dip switches are connected to the 80pin SCA connectors. That is where the disk gets its ID... Over the SCA connector (over the SCSI bus).
It doesnt get its ID from the controller card, that was a mistake. I did say a few posts ago how a backplane assigns its IDs to devices. The adapter I linked to in my first reply is a single disk SCA backplane. It looks a bit rough n ready but it is the same.