linux-ext4 - Question about enlarge ext4 more than 16T

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Date:   Tue, 26 Dec 2017 18:09:47 +0800
From:   rong zhao <zhaorbox@...il.com>
To:     linux-ext4@...r.kernel.org
Subject: Question about enlarge ext4 more than 16T

Hi,

  Recently, I met a problem when extending ext4.

At first, I cannot format ext4 more than 16T, then I upgraded
e2fsprogs to version 1.43.7 which is the latest stable version.

I can create more than 16T by command:

mke2fs -O 64bit -t ext4 /dev/mapper/xxx

After format it, I mount it under folder /nfs/xxx, it works good.

Then I find I cannot extend it online, steps:

1. lvextend to extend LVM size
2. resize2fs /dev/mapper/xxx, it reports cannot online resize
3. "dumpe2fs /dev/mapper/xxx | grep feature" command shows this
filesystem has no resize_inode flag

I tried many times and find if I created more than 16T, it has no
resize_inode flag, seems they are opposite, cannot enable at the same
time.

I find this page: https://bugzilla.redhat.com/show_bug.cgi?id=982871

According to this page, it seems on rhel7, it should be able to
enlarge online, but unfortunately, I failed on rhel6 and I can only
have rhel6.

If I umount /nfs/xxx first, then resize2fs can work expectedly,
however, this indicates we must stop our service for about 15~30
minutes. This is what I do not want.

Then I see there is an old patch talking about this issue:

https://patchwork.ozlabs.org/patch/256822/

>From this patch, it seems that extend ext4 for more than 16T is
possible, but I always fail on redhat 6.7.

At last, let me make a summary of my question:
1. if I create an ext4 FS more than 16T, it has no resize_inode flag,
so I cannot extend it online
2. if I create an ext4 FS less than 16T, even with -O 64bit option, I
cannot extend it to more than 16T, I tried online and offline

Please suggest, thank you very much.