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Date: Wed, 11 Dec 2013 08:09:02 +0000
From: Hugo Mills <hugo@carfax.org.uk>
To: Chris Murphy <lists@colorremedies.com>
Cc: Imran Geriskovan <imran.geriskovan@gmail.com>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: Feature Req: "mkfs.btrfs -d dup" option on single device
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On Tue, Dec 10, 2013 at 09:07:21PM -0700, Chris Murphy wrote:
> 
> On Dec 10, 2013, at 8:19 PM, Imran Geriskovan <imran.geriskovan@gmail.com> wrote:
> > 
> > Now the question is, is it a good practice to use "-M" for large filesystems?
> > Pros, Cons? What is the performance impact? Or any other possible impact?
> 
> Uncertain. man mkfs.btrfs says "Mix data and metadata chunks together for more efficient space utilization.  This feature incurs a performance penalty in larger filesystems.  It is recommended for use with filesystems of 1 GiB or smaller."

   That documentation needs tweaking. You need --mixed/-M for larger
filesystems than that. It's hard to say exactly where the optimal
boundary is, but somewhere around 16 GiB seems to be the dividing
point (8 GiB is in the "mostly going to cause you problems without it"
area). 16 GiB is what we have on the wiki, I think.

> I haven't benchmarked to quantify the penalty.

   Nor have I.

   Hugo.

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
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