Ric Wheeler wrote: > Alan Cox wrote: >>> First generation of 1K sector drives will continue to use the same >>> 512-byte ATA sector size you are familiar with. A single 512-byte >>> write will cause the drive to perform a read-modify-write cycle. >>> This configuration is physical 1K sector, logical 512b sector. >> >> The problem case is "read-modify-screwup" >> >> At that point we've trashed the block we were writing (a well studied >> recovery case), and we've blasted some previously sane, totally >> unrelated sector of data out of existance. Thats why we need to know >> ideally if they are doing the write to a different physical block when >> they do this, so that we don't lose the old data. My guess is they won't >> as it'll be hard. > > I think that the firmware would have to do this in the drive's write > cache and would always write the modified data back to the same physical > sector (unless a media error forces a sector remap). > > If firmware modifies the 7 512 byte sectors that it read to do the 1 512 > byte sector write, then we certainly would see what you describe happen. > > In general, it would seem to be a bad idea to do allocate a different > physical sector to underpin this king of read-modify-write since that > would kill contiguous layout of files, etc. > >>> A future configuration will change the logical ATA interface away >>> from 512-byte sectors to 1K or 4K. Here, it is impossible to read a >>> quantity smaller than 1K or 4K, whatever the sector size is. >> >> That one I'm not worried about - other than "guess how Redmond decide to >> make partition tables work" that one is mostly easy (be fun to see how >> many controllers simply can't cope with the command formats) >> > > This will be interesting to find out. I will be sharing a panel with > some BIOS & MS people, so I will update all on what I hear, Ric, Just to add a SCSI perspective, it looks like 4 KB sectored disks will be almost exclusively ATA devices. It is being done to improve capacity at the expensive of performance. [SCSI/FC/SAS disks typically trade off capacity for better performance.] Support for disks with smaller logical block size than physical block size has already been added to SBC-3. The overview of this document gives a rationale: www.t10.org/ftp/t10/document.06/06-034r5.pdf SAT is now a standard and an agenda item for SAT-2 is to wire ATA8-ACS's large sector size support to the additions to SBC-3 mentioned above. I'm not sure how this stuff plays with end to end data protection :-) Most SCSI disks currently allow formatting sizes of 512 up to 528 bytes per logical block. Doug Gilbert - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
