linux-ext4 - Reproducible block structure

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Date:	Mon, 9 Dec 2013 21:03:23 -0800
From:	Jitesh Shah <jitesh.1337@...il.com>
To:	linux-ext4@...r.kernel.org
Subject: Reproducible block structure

Hello all,
Assuming I have the latest ext4 system, I have a question ->
Scenario -> I have 5 HDDs on which I burn the same block image on.
These HDDs are usually mounted RO when used in production. For
upgrading, I connect each one to an isolated machine, mount it as RW
and run a script to update files (basically add, delete, modify
files).

Now, if the script is ran in the SAME way for all 5 HDDs, is it
guaranteed that these HDDs will be same at the block level too? (i.e.
block allocation/deallocation will follow the same pattern). Assume
single-core system with only one process modifying the HDD in
predetermined order.

If there is no way to provide such a guarantee in a default ext4
install, is there an ext4 option (ordered?) which can provide this
guarantee?

Why do I ask -> I am tinkering with the idea of block level
verification of images. If the above guarantees can be provided, I can
easily hash the raw HDD for verification purposes.

Thanks,
Jitesh

PS: I am not subscribed to the mailing list, so please include my id
in the response if your email client does not put it there already!
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