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Steve Livaccari wrote:
The concern is that the physical sectors on the drive will be misaligned with the file system clusters resulting in a drastic performance penalty, especially on writes.
This is a marketing problem...
On the hardware side... If some drive manufacturer is dumb enough to make a drive that has really poor performance on aligned accesses then they deserve what they get - no sales. I don't see how you can avoid less than optimun performance on unaligned accesses. Of course T13 could show some smarts here and define two new commands: READ and WRITE ALIGNED DMA that could be spec'ed as being invaild if the least significant bits of the starting LBA were not aligned and if the sector count was not proper multiple number of sectors.
On the host software side I don't know what to say. I'm sure there are OS and file system designers and implementers that understand the concept of aligning data properly for best performance. On the other hand we have a large OS vendor, that in my experience and opinion, has virtually no understanding of issues like this (why do they still start their C: partition at LBA 63?; and why did I get nothing but a blank response from them when I tried to discuss this issue with them some 5 years ago?).
The location and layout of data on the physical media of the device, be it magentic, flash memory, DRAM memory, or something else, has nothing to do with the presentation of that data at the interface when it is transferred by R/W commands. If I want to build a device that puts some of the data in flash, some on magentic media and some elsewhere, that doesn't matter as long as my device maintains data integrity and has useful function and performance so that there is a market for it.
Hale
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++ Hale Landis ++ www.ata-atapi.com ++
