tagged command queueing

[Eric NOULARD]

	I have some questions regarding tagged command queueing.

	1) Does all Adaptec aic7xxx base card support this feature?
	   I'm more concerned by:
		AHA 2940UW
	 	AHA 2910C
		AHA 2940AUA
           Is there anything to do with the Adaptec BIOS to enable/disable
           this feature? (I did not see any.)

	2) Does tagged command queueing improve performance when 
           only 1 device (a harddisk) is connected to the scsi card?
           How to measure the gain?

	3) Is it necessary when passing the aic7xxx=tag_info:{,,,} option
           to give a queue depth for the card itself?

	   More precisely, my cards have scsi Ids #7, should I enabled
           tagged command queueing on scsi Id #7.
	   Any advice or guideline to chose the depth of the queue for
           a specific device.

	4) Is it harmless to enable tag command queueing?

Finally, since all these questions just make clear how ignorant I am
regarding tagged command queueing, may be someone can give me a good URL or ref.
which explains how taggged command queueing work (in some detail).

	Thanks in advance.
	Eric


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