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Re: hole punching performance

To: "Bradley C. Kuszmaul" <kuszmaul@xxxxxxxxx>
Subject: Re: hole punching performance
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 16 Jan 2013 09:54:35 +1100
Cc: Florian Weimer <fw@xxxxxxxxxxxxx>, Ben Myers <bpm@xxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <CAKSyJXdejNhNgqq6g8N4n6Cjz2s3+m=JUvanTRfDtF72d2RxFg@xxxxxxxxxxxxxx>
References: <CAKSyJXf66H2U-BF-aYnSr2fF24_6LJw6swOx1RhUc_3Eqayaiw@xxxxxxxxxxxxxx> <87pq195t8q.fsf@xxxxxxxxxxxxxxxxx> <CAKSyJXfQsmemZ3H9A92UezsPCXfn37LXP3tpPMkiwtvR4=eY2g@xxxxxxxxxxxxxx> <20130113194941.GB27055@xxxxxxx> <20130113225545.GA19173@dastard> <87mwwaqgkj.fsf@xxxxxxxxxxxxxxxxx> <CAKSyJXdejNhNgqq6g8N4n6Cjz2s3+m=JUvanTRfDtF72d2RxFg@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Jan 15, 2013 at 04:34:50PM -0500, Bradley C. Kuszmaul wrote:
> So does it cost a lot to read all the extents just to read the first block?

Depends on the number of extents in the file. Figure an IO per 250
extents for a 4k block size filesystem (extent records are 16 bytes
in size on disk).

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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