32bit vs 64bit in the filesystem structures

[George R Goffe]

Howdy,

I'm trying to find out if there are any dependencies within the specific filesystem structures that are specific to 32bit and 64bit.

As far as I know you can mount a filesystem created on an x86_64 system on a x86 machine without any problems but this could just be that I have not been bitten yet and I'd rather avoid that if possible.

Is there a good place to go to find the answer to this question?

Regards and thanks for your time,

George...

"It's not what you know that hurts you, It's what you know that ain't so." Wil Rogers

[Rick Stevens]

On 04/21/2010 04:51 PM, George R Goffe wrote:
> Howdy,
>
> I'm trying to find out if there are any dependencies within the specific
> filesystem structures that are specific to 32bit and 64bit.
>
> As far as I know you can mount a filesystem created on an x86_64 system
> on a x86 machine without any problems but this could just be that I have
> not been bitten yet and I'd rather avoid that if possible.
>
> Is there a good place to go to find the answer to this question?

There should be no 32- vs. 64-bit dependencies in the implementation
of the ext2 or ext3 filesystems.  You should be fine.

The most common problem in the past was the use of a 32-bit "int"
instead of an "off_t" in the lseek() calls, which limited you to a 2GB
file size, but that's an application issue.

The ext2/ext3 filesystem limits are:

Filesystem block size:     1kB        2kB        4kB        8kB

File size limit:          16GB      256GB     2048GB     2048GB
Filesystem size limit:  2047GB     8192GB    16384GB    32768GB

Note that the 8kB blocksize was only available on the DEC Alpha, so
effectively the maximum filesystem size is 16TB.

There is also a limit of 32K subdirectories in a given directory and
there used to be an issue when the number of files grew above 10K
inside a directory (big slowdown...fixed with hashed directory entries).

With ext4, the 32K subdirectory limit is removed and it supports
filesystems larger than 16TB.  Not sure just how big, but BIG!  Not
sure if the e2fsutils stuff can handle filesystems >16TB yet.
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[Alan Cox]

On Wed, 21 Apr 2010 16:51:26 -0700 (PDT)
George R Goffe  wrote:
> Howdy,
>
> I'm trying to find out if there are any dependencies within the specific filesystem structures that are specific to 32bit and 64bit.
>
> As far as I know you can mount a filesystem created on an x86_64 system on a x86 machine without any problems but this could just be that I have not been bitten yet and I'd rather avoid that if possible.

That is certainly the intention.

Alan