[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: How do I fsck and XFS file system in "Squeeze"

Mark Allums put forth on 5/22/2010 8:32 PM:
> On 5/22/2010 2:22 AM, Stan Hoeppner wrote:
>> Mark Allums put forth on 5/21/2010 7:37 PM:
>>> 64-bit Knoppix is in the TODO list of Klaus Knopper, but for rescue
>>> purposes, 32-bit should be able to do the job.
>> This is incorrect _if_ the filesystem is large and thus contains 64
>> bit inode
>> numbers.  If there is any remote possibility that 64 bit inodes exist
>> on the
>> XFS filesystem to be checked/repaired, the rescue kernel and xfsprogs
>> need to
>> be 64 bit binaries.
> That's a very odd thing.  Thanks for correcting me.  I would not have
> guessed that file system structure would be dependent on OS word width.
>  I mean, that seems like a catastrophic implementation/design bug.

It's not an instruction word width issue, but has more to do with the width of
the data registers, and addressable virtual memory of 32bit platforms.

Running a 32bit kernel, how do you process 64bit inode numbers in 32bit data
registers?  That would require a lot of code changes for a dying platform
(ia32).  Add the fact that i386 kernels have a maximum virtual address space
of 16TB, which, not coincidentally, is the maximum 32bit XFS filesystem size.
 I think this last point is really the key to this issue, because if you were
to add support to 32bit XFS for 9 exabyte filesystems, you'd only be able to
mmap files up to the 16TB boundary.  AFAIK, most I/O these days is done with
mmap.  If you have files or filesystems larger than your virtual memory space,
you can't mmap anything beyond that address boundary.


Reply to: