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Re: How to format RAID1 correctly

To: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxxx>, xfs@xxxxxxxxxxx
Subject: Re: How to format RAID1 correctly
From: Helmut Tessarek <tessarek@xxxxxxxxxxx>
Date: Wed, 24 Sep 2014 11:53:54 -0400
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <542243E6.1040302@xxxxxxxxxxxxxxxxx>
References: <5422146A.90206@xxxxxxxxxxx> <54222763.40107@xxxxxxxxxxx> <5422285B.6010306@xxxxxxxxxxx> <542234F6.4080000@xxxxxxxxxxxxxxxxx> <5422376D.3000204@xxxxxxxxxxx> <542243E6.1040302@xxxxxxxxxxxxxxxxx>
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On 2014-09-24 0:09, Stan Hoeppner wrote:
> If you create any striped arrays, especially parity arrays, with md make
> sure to manually specify chunk size and match it to your workload.  The
> current default is 512KB.  This is too large for a great many workloads,
> specifically those that are metadata heavy or manipulate many small
> files.  512KB wastes space and with parity arrays causes RMW, hammering
> throughput and increasing latency.

Thanks again for the valueable information.

I used to work with databases on storage subsystems, so placing GBs of
database containers for tableapaces on arrays with a larger stripe size
was actually beneficial.
For log files and other data I usually used different cache settings and
strip sizes.

So how does this work with SW RAID?

Does the XFS chunk size equal the amount of data touched by a single r/w
I'm asking because data is usually written in page/extent sizes for
databases. Even if I have a container with 50GB, I might only have to
read/write a 4k page.

 K. C.

regards Helmut K. C. Tessarek
lookup http://sks.pkqs.net for KeyID 0xC11F128D

   Thou shalt not follow the NULL pointer for chaos and madness
   await thee at its end.

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