SCSI_ADDRESS structure says:
PortNumber : Identifies the SCSI controller.
PathId : Identifies the bus on the SCSI controller.
TargetId : Identifies the target device on the SCSI bus.
Lun : Identifies the individual logical unit at the target device specified by TargetId.
i.e. Bus number is the identifier in the SCSI controller. Not the bus in Windows.
But the port number is an unique number of the SCSI port device object.
I think it is too tricky to say the same load conditions.
Especially, disk performance is heavily affected by the positions of sectors
where you want to access. I don’t know how to explain your results good enough.
Disable Tagged queuing and synchronous transfer mode when measuring the performance
if the parallel transfer matters.
Regards,
Chesong Lee
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Arijit Bhattacharyya
Sent: Thursday, November 24, 2005 6:22 AM
To: Windows File Systems Devs Interest List
Subject: Re: [ntfsd] SCSI targets having same IDs and LUNs
Hi
Ok…I got ur point. The disk management utility shows Location of a disk as: Bus number + Target ID + LUN. I compared this bus number with the Path ID that I get from IOCTL_SCSI_GET_ADDRESS and they somehow seem to be the same. Hence the conclusion. It would be great if you can explain what this bus number means. Apart from this, I have another question which is more important to me:
I have 8 SCSI disks. And they have almost the same write speed. But suppose I just select 5 disks from these 8 disks and write to them parallely, I get very different results for the total write speed with different subsets of 5 disks. And I am comparing the speeds with same load conditions. I am trying to figure out why this is happening and I have a strong hunch that it is dependent on the layout of these disks. Also, one more thing…i have 3 SCSI controllers in my system. Can anyone solve this anomaly?
regards and thanks again.
On 11/24/05, Chesong Lee wrote:
SCSI_ADDRESS have PortNumber, PathId, TargetId and Lun only.
Where did you get the bus number?
AFAIK, SCSI Port Number is the number for opening the actual scsi port as a symbolic link as a form of
“\.\Scsi%d:” (e.g. \.\Scsi1:, \.\Scsi2: ). I haven’t found the formal definition of it yet.
If disks have different scsi port numbers, those are attached to different scsi port devices. 
(SCSI Port devices include IDE ports.) The device identification should be (port,target,lun) tuples (excluding pathid).
not (target id, lun). And again SCSI_ADDRESS does not have bus number.
SCSI controllers may have multiple scsi port devices, which may explain why you have different port numbers.
Regards,
Chesong Lee
________________________________
From: xxxxx@lists.osr.com [mailto: xxxxx@lists.osr.com mailto:xxxxx] On Behalf Of Arijit Bhattacharyya
Sent: Thursday, November 24, 2005 5:33 AM
To: Windows File Systems Devs Interest List
Subject: [ntfsd] SCSI targets having same IDs and LUNs
Hi
I am using the IOCTL_SCSI_GET_ADDRESS and seeing that two SCSI harddisks have the same Target ID, bus number and LUN. There SCSI port numbers are different. This is very surprising since I was expecting a unique combination of TargetID+LUN for each device that is present on the same SCSI bus. I dont at all understand the meaning of SCSI port number here. Can anyone help me out to understand the underlying architecture?
I would think that having the SCSI harddisks daisy chained, with a unique target ID and a LUN=0 would give me better write performance on these disks. I am comparing with the present scenario. Of course I cannot have a total of more than 16 SCSI devices connected to the same HBA. Can anyone comment on this?
Thanks in advance.
regards
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