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Re: extremely slow write performance plaintext

To: Mathieu AVILA <mathieu.avila@xxxxxxxxxxxxxxxx>
Subject: Re: extremely slow write performance plaintext
From: Cory Coager <ccoager@xxxxxxxxxxxxxxx>
Date: Tue, 25 Jan 2011 09:25:11 -0500
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Cc: xfs@xxxxxxxxxxx
In-reply-to: <4D3E9C73.6090508@xxxxxxxxxxxxxxxx>
Organization: Davis Vision
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On 01/25/2011 04:48 AM, Mathieu AVILA wrote
You're getting 40MB/s write speed and says that's fine? I get more
performance from a single SATA desktop drive. Your setup seems to suck
extremely somewhere.

It already starts with your dd speed. I started it on a virtualized VM
on an old, overloaded server and get:

# dd if=/dev/zero of=test.dd bs=1k count=1M
1048576+0 Datensätze ein
1048576+0 Datensätze aus
1073741824 Bytes (1,1 GB) kopiert, 10,9992 s, 97,6 MB/s

I would say this is melted with cache hit, isn't it ? (although I agree it depends on the server's memory dedicated to FS cache)

A real cache hit on a real server would give me at least 500 MB/s (actually I get something around 1 GB/s) When it starts to be disk-constrained, on a standard SATA disk, I get from 75 MB/s to 140 MB/s depending on the position of the AG I hit.
I agree, it should be a lot faster even on the LV's that are functioning fine. The disk arrays and disks are new but the rest of the hardware is pretty old, that might be part of the problem. It is a ProLiant DL385 G1.

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