From: Eric Sandeen <sandeen@redhat.com>
Subject: Re: More testing: 4x parallel 2G writes, sequential reads
Date: Wed, 07 Nov 2007 17:18:31 -0600
Message-ID: <473247C7.4020101@redhat.com>
References: <47323F73.5080708@redhat.com> <20071107230905.GQ3966@webber.adilger.int>
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To: Eric Sandeen <sandeen@redhat.com>,
	ext4 development <linux-ext4@vger.kernel.org>
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Andreas Dilger wrote:

> The question is what the "best" result is for this kind of workload?
> In HPC applications the common case is that you will also have the data
> files read back in parallel instead of serially.

Agreed, I'm not trying to argue what's better or worse, I'm just seeing
what it's doing.

The main reason I did sequential reads back is that it more clearly
shows the file layout for each file on the graph.  :)  I'm just getting
a handle on how the allocations are going for various types of writes.

> The test shows ext4 finishing marginally faster in the write case, and
> marginally slower in the read case.  What happens if you have 4 parallel
> readers?

I'll test that a bit later (have to run now); I expect parallel readers
may go faster, since the blocks are interleaved, and it might be able to
suck them up pretty much in order across all 4 files.

I'd also like to test some of this under a single head, rather than on
HW raid...

-Eric