Re: [Qemu-devel] [PATCH RFC] Advertise IDE physical block size as 4K

[Christoph Hellwig <hch@lst.de>]

On Tue, Dec 29, 2009 at 02:39:38PM +0100, Luca Tettamanti wrote:
> Linux tools put the first partition at sector 63 (512-byte) to retain
> compatibility with Windows;

Well, some of them, and depending on the exact disks.  It's all rather
complicated.

> > It has been discussed for hardware disk design with 4k sectors, and
> > somehow there were plans to map sectors so that the Linux partition
> > scheme results in nicely aligned filesystem blocks
> 
> Ugh, I hope you're wrong ;-) AFAICS remapping will lead only to
> headaches... Linux does not have any problem with aligned partitions.

Linux doesn't care.  As doesn't windows.  But performance on mis-aligned
partitions will suck badly - both on 4k sector drives, SSDs or probably
various copy on write layers in virtualization once you hit the worst
case.  Fortunately the block topology information present in recent
ATA and SCSI standards allows the storage hardware to tell about the
required alignment, and Linux now has a topology API to expose it, which
is used by the most recent versions of the partitioning tools and
filesystem creation tools.