Messages in this thread |  | | Date | Thu, 19 Sep 1996 11:25:06 -0700 | From | "Leonard N. Zubkoff" <> | Subject | Re: more on AHA-2940UW vs. MSDOS file system |
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From: Harold A Czegledi <hac@thinkage.on.ca> Date: Thu, 19 Sep 1996 10:05:25 -0400 (EDT)
I've observed this behaviour as well on the 2GB wide Quantum Atlas. A test I performed, with tagged queuing enabled and with the maximum number of tagged SCSI commands set to one, resulted in a QUEUE_FULL status every 38 I/O's when doing a one block I/O operation. Setting the FUA bit within the 10-byte SCSI SCB "fixed" the problem but at a substantial cost to overall I/O throughput. As a result, I think a switch to a Seagate Barracuda may be in order - hopefully, it does not exhibit the same sort of behaviour.
QUEUE FULL is a perfectly valid status for a drive to return. If a host adapter's firmware or the driver's sequencer logic does not handle this condition, then it ought not to be using tagged queuing at all. Assuming that any specific number of outstanding commands will always be accepted is broken.
Leonard
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