Re: ext2 large block size > page size

[Mason <mpeg.blue@free.fr>]

[ Adding Christoph Lameter to the CC list ]

Hello Ted,

Ted Ts'o wrote:

> On Tue, Mar 29, 2011 at 01:52:38PM +0200, Mason wrote:
>
>> 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.

Unfortunately, the operating system of the set-top box
is not Linux (ST has only very recently started migrating
to Linux).

Their "legacy" OS (OS+ running on top of OS21) provides
(proprietary, I suppose) implementations of FAT32 and ext2.

I used to create FAT32 partitions, until I plugged a 2-TB
USB HDD in the STB:
format = 123 s
mount  =  62 s
fsck   = 517 s (!!)

I switched to ext2, hoping to avoid the need to fsck, thanks
to the soft updates mode. Problem is, I can't read the files
on a Linux PC if I use large blocks, and performance takes a
dive if I use "normal" blocks.

> 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.

Unfortunately, the mount function in this OS accepts only
two flags: RDONLY and RDWR :-(

If I understand correctly, I'm screwed, right? :-)

-- 
Regards.