[Openstack-operators] Configuring local instance storage

Arne Wiebalck Arne.Wiebalck at cern.ch
Fri May 9 09:50:00 UTC 2014

Any experiences with "unexpected" SSD failures, i.e. failures that were not predicted? I am asking this
as we're considering to use block level caching on non-RAIDed SSDs and I'd like to get a feeling for
how much we have to reflect this in the SLA :) 


On May 9, 2014, at 8:13 AM, Robert van Leeuwen <Robert.vanLeeuwen at spilgames.com> wrote:

> 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 :)
> Cheers,
> 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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