GPT and disk alignment
numisemis at gmail.com
Wed Jun 8 07:26:01 UTC 2011
2011/6/8 Robert Simmons <rsimmons0 at gmail.com> wrote:
> Ok, but can I assume that all HDDs of this type expand each of the 4K
sectors so that physically they take up the same space as eight 512
> byte LBAs? AFAIK, the new 4K LBA has a smaller ECC area than the sum
> of 8 ECC areas in 512 byte LBAs, so if the data area was _not_
> expanded slightly, you would never really be aligned except every x
> LBAs as the shifting approaches an LBA boundary, right?
Wrong, leave ECC out of the equation.
ECC size is totally transparent and hidden to everything except the drive
Sector sizes that drives present to outside world contain only data part, so
512 or 4K is the size of data part.
> For any HDDs, do I need to worry about cylinder boundaries at all?
> Has the reported "disk geometry" become divorced from the physical
> reality in modern disks? If I do still need to worry about cylinder
> boundaries, should I basically ignore every reported geometry (BIOS,
> OS) and use what is written on the sticker on the drive?
> Can I just ignore the idea of "cylinder boundaries" completely when
> dealing with SSDs and flash memory?
Ignore geometries and cylinder boundaries for all of them (modern hard
drives, SSD and flash memory). Those exist only for compatibility reasons.
Physical drive geometry on modern hard drives is hidden (and probably is
asymmetric), so there is no point in trying to optimize by using cylinder
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