Re: ext2 large block size > page size

[Ted Ts'o <tytso@mit.edu>]

On Tue, Mar 29, 2011 at 01:52:38PM +0200, Mason wrote:
> Hello everyone,
> 
> As far as I can tell from a quick Google search,
> there was a push in 2007 to add support for large
> blocks in some file-systems, in particular ext2.
> 
> e.g. cf. http://lwn.net/Articles/239090/
> 
> Was this ever accepted into the main line?
> (It seems to have lived within -mm for a while)

Nope, it never was (as you've by now figured out).

> I'm working with a ST Microelectronics set-top box.
> Here are a few performance results for a 2TB USB HDD:
> block size  4k  :  format = 151 s / mount = 242 s
> block size  8k  :  format =  52 s / mount =  71 s
> block size 16k  :  format =  30 s / mount =  36 s
> block size 32k  :  format =  18 s / mount =  19 s
> 
> Using 4kB blocks makes mount too slow on the STB, which
> is why I'd like to use larger blocks. It would be nice
> if the movies recorded on the STB could also be read on
> a Linux PC.

My guess is the mount time slowness is caused an ancient kernel
running on the ST Microelectronics box which is doing mount-time
sanity checks.  You can disable this with the mount option -o nocheck.

A lot of the rationale for larger block sizes was obviated by the use
of more advanced file systems, such as ext4, which have other methods
of dealing with the inefficiencies caused by smaller block sizes.  If
your main complaint with using a 4k block size on the set-top box was
the mount-time slowness, that can be fixed with the nocheck mount
option.

Regards,

							- Ted