Re: Beating a dead horse

[Andreas Gustafsson <gson%gson.org@localhost>]

Greg Troxel wrote:
> > I would go further than that.  Alignment is not only an issue with 4K
> > sector disks, but also with SSDs, USB sticks, and SD cards, all of
> > which are being deployed in sizes smaller than 128 GB even today.
> 
> I didn't realize that.  Do these devices have 4K native sectors?

The don't have sectors as much as flash pages, and the page size
varies from device to device.  For example, Intel Datacenter SSDs have
either 8 KB or 16 KB pages according to this document:

  http://www.intel.com/content/dam/www/public/us/en/documents/technology-briefs/ssd-partition-alignment-tech-brief.pdf

> So you mean 2048 for >= 1G?

Yes.

> Is there a clear motivation for 2048 vs 64?   Are there any known
> devices where that matters?

Intel specifically recommends 1 MB alignment (2048 sectors) in the
document linked above.  Also, 128 kB is a common erase block size in
consumer flash media, but I'm not sure how relevant that is to
partition alignment.

> But why is just changing 63 to 64 always an issue?  Or using that for
> >= 1G?   Other than complexity, and having 3 branches.

I don't have a problem with changing the 63 to 64 for the smallest
devices, or with having 3 branches.  I would just like an 80 GB SSD,
for example, to get get aligned to 1 MB per Intel's recommendation.
-- 
Andreas Gustafsson, gson%gson.org@localhost