[Openstack-operators] Configuring local instance storage

Robert van Leeuwen Robert.vanLeeuwen at spilgames.com
Fri May 9 06:13:29 UTC 2014

We are using KVM.
What I noticed on the hypervisor was that it was actually doing lots of reads when doing the benchmark on QCOW2 images.
I simulated a MYSQL workload on the OS, I created a 20GB file and doing 100% random 16K write IOPS in it.
On QCOW we got about 600 IOPS on RAW about 5000. 
With RAW we did no reads when writing while with QCOW I saw 100MB+ reads per second.
I would be happy to know if we can improve this somehow :)

We are monitoring the lifetime of the SSDs and will do some preventive swapping:
There are lifetime estimations you can read from the SSDs.
Luckily the array controller we have lets us query those stats per disk even if they are in RAID :)

Robert van Leeuwen

From: Abel Lopez [alopgeek at gmail.com]
Sent: Thursday, May 08, 2014 9:50 PM
To: Tim Bell
Cc: Robert van Leeuwen; Arne Wiebalck; openstack-operators at lists.openstack.org
Subject: Re: [Openstack-operators] Configuring local instance storage

Second that question, Using KVM at least, I couldn't find any significant differences between QCOW2 and RAW based images.
By "significant", I mean, enough to justify tossing the benefits of qcow2.

On May 8, 2014, at 8:57 AM, Tim Bell <Tim.Bell at cern.ch> wrote:

> Robert,
> The difference between RAW and QCOW2 is pretty significant... what hypervisor are you using ?
> Have you seen scenarios where the two SSDs are failing at the same time ? Red Hat was recommending against mirroring SSDs as with the same write pattern, the failure points for the same batch of SSDs would be close.
> Tim
> -----Original Message-----

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