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Date: Wed, 11 Apr 2018 09:39:48 +1000
From: Dave Chinner <david@fromorbit.com>
To: Sayan Ghosh <sgdgp.2014@gmail.com>
Cc: Andreas Dilger <adilger@dilger.ca>,
        "Theodore Y. Ts'o" <tytso@mit.edu>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>,
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        Madhumita Mallick <madhu.cse.ju@gmail.com>,
        "Bharde, Madhumita" <madhumita.bharde@hpe.com>
Subject: Re: [Patch 0/4] RFC : Support for data gradation of a single file.
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On Tue, Apr 10, 2018 at 03:26:11PM +0530, Sayan Ghosh wrote:
> > That said, having a hard-coded separation of flash vs. disks does not
> > make sense, even from an intermediate development point of view.  There
> > definitely should be a block-device interface for querying what the
> > actual layout is, perhaps something like the SMR zones?
> 
> Yes, I agree, that the ideal situation would be to have a mechanism to
> identify the segment boundaries automatically inside the LVM. But we
> were not able to get a method to access the boundaries or rather the
> location of a free block in each segment by such system call.
> So, in order to just test out the system we proceeded by hardcoding
> the boundaries as per our simulated LVM. But since this is not
> practical we provided the TODO/FIX IT in those areas. We are still
> looking for a good mechanism, and would welcome any
> advice/suggestions.
> 
> Also, we chose to use Ext4 since it is generally the most commonly
> used file system in linux based systems. However, I am not aware if
> the problem of getting the boundaries can be solved in a simpler
> manner by using XFS.

SSD for the data device, HDD for the realtime device, device
auto-selection based on initial allocation size patchset like this
one:

https://marc.info/?l=linux-xfs&m=151190613327238&w=2

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com