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Re: XFS/LVM/Multipath on a single RAID volume

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: XFS/LVM/Multipath on a single RAID volume
From: Emmanuel Florac <eflorac@xxxxxxxxxxxxxx>
Date: Wed, 25 Feb 2015 12:49:46 +0100
Cc: Dave Hall <kdhall@xxxxxxxxxxxxxx>, stan@xxxxxxxxxxxxxxxxx, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20150224223344.GE4251@dastard>
Organization: Intellique
References: <5155F2B2.1010308@xxxxxxxxxxxxxx> <20130331012231.GJ6369@dastard> <515C3BF3.60601@xxxxxxxxxxxxxx> <51684382.50008@xxxxxxxxxxxxxx> <5168AC0B.5010100@xxxxxxxxxxxxxxxxx> <516C649A.8010003@xxxxxxxxxxxxxx> <20130416161841.GB13938@destitution> <54EA67B7.30805@xxxxxxxxxxxxxx> <20150223121812.5077ff07@xxxxxxxxxxxxxxxxxxxx> <54ECF573.9050106@xxxxxxxxxxxxxx> <20150224223344.GE4251@dastard>
Le Wed, 25 Feb 2015 09:33:44 +1100
Dave Chinner <david@xxxxxxxxxxxxx> Ãcrivait:

> > On an existing array based on similar but slightly slower hardware,
> > I'm getting miserable performance.  The bottleneck seems to be on
> > the server side.  For specifics, the array is laid out as a single
> > 26TB volume and attached by a single 3Gbps SAS.   
> So, 300MB/s max throughput.

Ah yes, maybe external RAID controllers can only use one SAS channel
out of the 4 available, that would definitely limit performance badly.
This limitation don't apply to internal RAID controllers (Adaptec, LSI,
Areca) driving a JBOD though.

I'll do a short digression on external storage enclosures: they're
mostly useful to provide redundant controllers. If you're using only one
controller, cheap ones (such as infortrend, Promise and the like) will
always perform poorly compared to a modern PCIe RAID controller.

High-end storage enclosures (DotHill, NetApp, etc) with high-bandwidth
attachments (FC or IB) provide better performance AND redundancy, but
at a hefty price.

So if you want fast, cheap arrays, definitely use Adaptec/LSI/Areca and
simple JBOD chassis like supermicro's.

Emmanuel Florac     |   Direction technique
                    |   Intellique
                    |   <eflorac@xxxxxxxxxxxxxx>
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