Subject: Re: bug#69535: Problem with copying an EXTREMELY large file - cmp finds a mismatch

From: Brian <[email-masked]>
Date: Mon, 4 Mar 2024 03:53:44 -0500

On 3/4/24 03:10, Paul Eggert wrote:
> Try running 'strace -o tr cp data.dat original' and then look at the 
> file 'tr' (which could be quite large). Look for the syscalls near the 
> start, and near the end, of the bulk copy.
> 
> Quite possibly it's a bug in your Linux drivers or your firmware or 
> hardware. For example, if you're using ZFS, see:
> 
> https://github.com/openzfs/zfs/issues/15526
> 
> The strace output might help figure this out.

My drives are formatted using ext4. The command above did indeed 
produce a large output file, almost 40 Megabytes of it, but deleting 
every line that started with

read(3,

or

write(4,

(there were over 300,000 pairs) got the file down to a far more 
manageable 7 KB. At first glance, it doesn't make much sense to me, 
but I will try going through it line-by-line tomorrow (it's silly 
o'clock at the moment) and see whether anything jumps out at me.

Thanks for the help.