The origin of SCSI [WAS:RE: The origin of the phrases ATA and IDE ]

Peter Coghlan cctalk at beyondthepale.ie
Thu Oct 5 18:23:48 CDT 2017



>
> The biggest problem you had was the requirement to assert ATN when 
> selected properly.  Later the tag queuing caused huge headaches as 
> manufacturers implemented that feature.
>
> It eventually was made mandatory for the most part by linux, and perhaps 
> Windows requiring the tag queuing drilled own to the lowest level of the 
> system's use of the disk.  The capability to do that, or fake it is 
> required to allow the kernel to queue commands to run, and have the OS 
> continue to run till command completion.
>

I recall VMS having issues with SCSI disks which claimed to do tag queueing
(and bad block replacement) but didn't do it right, before I'd even heard
of linux.

Customers complained that VMS refused to work with commodity SCSI disks
and thought that it was a conspiracy to get them to buy expensive DEC branded
disks.  DEC claimed that only the disks with their firmware did tag queueing
and bad block replacement correctly.  The VMS SCSI driver supposedly had (has?)
a list of specific disks known to mess up which it would refuse to bring
online.

I wasn't well up on Sun but I expect the same issue existed there too.

Regards,
Peter Coghlan.


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