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Re: block alignment

To: xfs@xxxxxxxxxxx
Subject: Re: block alignment
From: Ric Wheeler <rwheeler@xxxxxxxxxx>
Date: Mon, 07 Jan 2013 16:47:29 -0500
In-reply-to: <CAKSyJXdP0NSQrR+rfrCec+oCyVg-2SRmCmYf3V7kjC1-0x49bA@xxxxxxxxxxxxxx>
References: <CAKSyJXdP0NSQrR+rfrCec+oCyVg-2SRmCmYf3V7kjC1-0x49bA@xxxxxxxxxxxxxx>
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On 01/07/2013 04:33 PM, Bradley C. Kuszmaul wrote:
What is the largest data block size that I'm likely to run into with xfs?

I ask, since I'm doing hole punching, and I don't want to incur the I/O required to zero unaligned boundaries. So I want to keep the holes I punch sufficiently well aligned.


I think that you really need to worry about the block sizes below XFS - the storage block size specifically. Upstream (and modern distros like RHEL/SLES/etc) do work to export out alignment requirements and optimal IO sizes.

You can find them in /sys/block/sda/. Martin Peterson wrote up a good overview of what we have in there:



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