linux-ext4 - 1024TB Ext4 partition

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Date:   Thu, 24 Oct 2019 16:23:15 +0300
From:   Благодаренко Артём 
        <artem.blagodarenko@...il.com>
To:     linux-ext4 <linux-ext4@...r.kernel.org>
Cc:     Andreas Dilger <adilger@...ger.ca>,
        "Theodore Y. Ts'o" <tytso@....edu>
Subject: 1024TB Ext4 partition

Hello,

Lustre FS successfully uses LDISKFS(ext4) partitions with size near 512TB.
This 512TB is current "verified limit". This means that we do not expect any troubles in
production with such large partitions.

Our new challenge now is 1024TB because hardware allows to assemble such partition.
The question is: do you know any possible issues with EXT4 (and e2fsprogs) for such large partitions?

I know about this possible problems:
1. E2fsck is too slow. But parallel e2fsck project is being developed by Li Xi
2. Block groups reading takes a lot of time. We have fixes for special cases like e2label. 
    Bigalloc also allows to decrease metadata size, but sometimes meta_bg is preferable.
3. Aged fs and allocator that process all groups to find good group. There is solution, but with some issues.
4. 32 bit inode counter. Not a problem for Lustre FS users, that prefer use DNE for inode scaling,
    but probably somebody wants to store a lot inodes on the same partition. Project was not finished.
    Looks nobody require it now.

Could you please, point me to other possible problems?

Thanks.
Artem Blagodarenko.