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Hale, IIRC when Nina from Microsoft intoduced this monster, many issues came up. The worst was FUA would ram to the front of the cache queue and basically NUKE all outstanding tags. This was a major mess. Corrections requested. Andre Hedrick LAD Storage Consulting Group On Mon, 16 Jun 2003, Hale Landis wrote: > This message is from the T13 list server. > > > As I asked in the previous email, I don't see a proposal for the > WRITE DMA QUEUED FUA command. But looking at the ATA/ATAPI-7 > description (both the general description of O/Q and the command > description) I don't see a problem. Basically this command is a O/Q > command (so it does not abort the outstanding command queue) but it > is a command that is not allowed to release (so it executes like an > non-O/Q command). Yes, that may be a big performance problem but that > is the price you pay. > > HOWEVER, there is a big problem if the host is dumb and has > outstanding O/Q commands, read and/or write, that access the same > sectors that another O/Q command accesses (including the WRITE DMA > QUEUED FUA command). Again, unless I missed something, I think > ATA/ATAPI-x has nothing to say about the action and/or data integrity > of O/Q commands that access the same sectors. I think when O/Q was > added for hard disk drives T13 assumed this was the host's problem. > > But the O/Q EXT commands have yet another problem (that I have asked > about before). If these commands are used with really large transfer > lengths (remember that and EXT command can tranfer up to 65536 > secotors or about 33Mbytes of data) these commands have a real > performance problem in that only one release/service cycle is allowed > (and that must be before any data is tranferred). The ATAPI DMA O/Q > option of the PACKET command allows a device to release/service > multiple times (before and during the data transfer). O/Q EXT > commands should allow the same for hard disk drives. > > Now the "real" question... Does any of this O/Q stuff matter? Doesn't > SATA have something that replaces all this old PATA O/Q stuff? > > Hale > > > > *** Hale Landis *** www.ata-atapi.com *** > > >
