This message is from the T13 list server.
On Fri, 27 Jun 2003 09:13:02 -0700, Nathan Obr wrote: >This message is from the T13 list server. >Hale, >I don't understand your interest of a disk drive cache >algorithm. The only behavior the host can assume about a disk cache is >that it doesn't change the behavior of the drive. Once the drive has >signaled the completion of a transfer, it doesn't matter to the host >where the data physically lives as long as the next time it does a read, >it gets the same data back. But you are assuming the drive manufacturers will do the "right thing". Since T13 and ATA/ATAPI-x don't say what the "right thing" is you are subject to different interpretation of the "right thing". And trust me, I could come up with probably 3 different algorithms for the write cache, all "valid" per ATA/ATAPI-x, but a read to write cached data would return different data. You are assuming a specific but undocumented implementation from every drive manufacturer. >Because the FUA commands do not affect the internal queuing or >write ordering of the disk, FUA commands are no more of a data integrity >problem for the host then normal write and queued write commands. In >fact, FUA commands don't even affect the caching on the disk. FUA data >transfers can still be cached, they just can't be signaled complete >until the command is written to disk. I think there are some disk designers that would disagree about the effect of FUA on the drive's internal operation, especially the effect on read and write cached data. Remember that many drives execute commands (or most of a command) via hardware sequencers these days. Hale *** Hale Landis *** www.ata-atapi.com ***
