Re: [gentoo-user] 1-Terabyte drives - 4K sector sizes? -> bar performance so far

[Willie Wong]

On Tue, Feb 09, 2010 at 01:05:11AM +0100, Frank Steinmetzger wrote:
> Am Sonntag, 7. Februar 2010 schrieb Mark Knecht:
>
> > Hi Willie,
> >    OK - it turns out if I start fdisk using the -u option it show me
> > sector numbers. Looking at the original partition put on just using
> > default values it had the starting sector was 63
>
> Same here.
>
> > - probably about the worst value it could be.
>
> Hm.... what about those first 62 sectors?

It is possible you can use some of those; I never tried. That's a
negligible amount of space on modern harddrives anyway. And actually,
starting on sector number 63 means that you are skipping 63 sectors,
not 62, since LBA numbering starts with 0. 

Historically there is a reason for all drives coming with default
formatting with the first partition at section 63. Sector 0 is the
MBR, which you shouldn't overwrite. MSDOS and all Windows up to XP
requires the partitions be aligned on Cylinder boundary. So it is
safest to just partition the drive, by default, such that the first
partition starts at LBA 63, or the 64th sector, or the first sector of
the second cylinder. 

Actually, this is why Western Digital et al are releasing this flood
of 4K physical sector discs now. Windows XP has been EOLed and Vista
and up supports partitioning not on cylinder boundary. If Windows XP
still had support, this order of magnitude inefficiency wouldn't have
been overlooked by most consumers. 

> I bought this 500GB drive for my laptop recently and did a fresh partitioning
> scheme on it, and then rsynced the filesystems of the old, smaller drive onto
> it. The first two partitions are ntfs, but I believe they also use cluster
> sizes of 4k by default. So technically I could repartition everything and
> then restore the contents from my backup drive.

Are you sharing the harddrive with a Windows operating system?
Especially Windows XP? There are reports that Windows XP supports
partitioning not aligned to cylinder boundary. However, if you are
dual booting you will almost surely be fscked if you try that. I had
some fun earlier last year when I did everything else right but
couldn't figure out why my laptop tells me it cannot find the
operating system when I tried to dual boot. 

> Though the result justifies your decision, I would have though one has to
> start at 65, unless the disk starts counting its sectors at 0.

I've always assumed by default that computer programmers starts
counting at 0. Mathematicians, on the other hand, varies: analysts
start at 0 or minus infinity; number theorists at 1; algebraists at 1
for groups but 0 for rings; and logicians start counting at the empty
set. :)

Cheers, 

W
-- 
Willie W. Wong                                     wwong@××××××××××××××.edu
Data aequatione quotcunque fluentes quantitae involvente fluxiones invenire 
         et vice versa   ~~~  I. Newton