linux-kernel - Re: [PATCH 2/2] Btrfs-progs: Add hot data support in mkfs

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Message-Id: <201009011356.51609.hka@qbs.com.pl>
Date:	Wed, 1 Sep 2010 13:56:49 +0200
From:	Hubert Kario <hka@....com.pl>
To:	Ben Chociej <bchociej@...il.com>
Cc:	chris.mason@...cle.com, linux-btrfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	cmm@...ibm.com, bcchocie@...ibm.com, mrlupfer@...ibm.com,
	crscott@...ibm.com, mlupfer@...il.com, conscott@...edu
Subject: Re: [PATCH 2/2] Btrfs-progs: Add hot data support in mkfs

On Friday 13 August 2010 16:10:24 Ben Chociej wrote:
> It's a good point, of course. Ideally we would be able to prioritize
> data and place them on 15k versus 7.2krpm disks, etc. However you get
> to a point where's there's only incremental benefit. For that reason,
> the scope of this project was simply to take advantage of SSD and HDD
> in hybrid. Of course, you could register the same complaint about the
> ZFS SSD caching: why not take advantage of faster vs. slower spinning
> disks? Unfortunately it just wasn't in the scope of our 12-week
> project here.
> 
> That's not to say it *shouldn't* be done in the future, of course!
> And, incidentally, you could hack it together at this point by setting
> the /sys/block/<blockdev>/queue/rotational flag to 0 and using it like
> an SSD. :)

Then why not make the devices with rotational at 0 be the default "SSDs" but 
allow the admin to set manually others, without hacking?

You can have SSDs in a hardware RAID array, this way the kernel may not know 
if the block device is on flash media or on rotational media...

-- 
Hubert Kario
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