Message-ID: <43224ABB.3030002@vgertech.com>
Date: Sat, 10 Sep 2005 03:53:47 +0100
From: Nuno Silva <nuno.silva@vgertech.com>
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To: Eyal Lebedinsky <eyal@eyal.emu.id.au>
CC: list linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: RAID resync speed
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Hi,

Eyal Lebedinsky wrote:
> I noticed that my 3-disk RAID was syncing at about 40MB/s, now that I
> added a fourth disk it goes at only 20+MB/s. This is on an idle machine.

3*40=120

4*20=80


> Individually, each disk measures 60+MB/s with hdparm.


And concurrent hdparms? Or some dd's concurrently?


> kernel: 2.6.13 on ia32
> Controller: Promise SATAII150 TX4
> Disks: WD 320GB SATA
> 
> Q: Is this the way the raid code works? The way the disk-io is managed? Or
> could it be due to the SATA controller?

You can isolate the performance drop with some dd's. Maybe this card is 
in a pci32/33mhz and you're hitting the pci bus' limits? (120~130MB/sec).

Regards,
Nuno Silva

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