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ag selection

To: linux-xfs@xxxxxxxxxxx
Subject: ag selection
From: Bernd Schubert <bernd.schubert@xxxxxxxxxxxxxxxxxx>
Date: Mon, 11 Nov 2013 18:25:13 +0100
Delivered-to: linux-xfs@xxxxxxxxxxx
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Hi all,

for streaming writes onto a raid6 the current round-robin ag selection seems does not seem to be optimal. Writing 4 files from 4 threads into a single directory we get 900 MB/s, writing 4 files in 4 different directories we only get 700 MB/s (12 disks with with hw megaraid-sas). The current round-robin scheme seems to be optimized for linear raid0? With small AGs one could also argue, that choosing AGs which are not far away from each other (in respect to the number of blocks) also adds more parallel disk access for small and medium sized files.

Any objections against a patch to improve the AG selection?


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