x2 replication is perfectly fine as long as you also keep min_size at 2 ;)
(But that means you're offline as soon as something is offline)
Paul
--
Paul Emmerich
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On Wed, Feb 19, 2020 at 4:41 PM Wido den Hollander <wido(a)42on.com> wrote:
>
>
>
> On 2/19/20 3:17 PM, Frank R wrote:
> > Hi all,
> >
> > I have noticed that RedHat is willing to support 2x replication with
> > NVME drives. Additionally, I have seen CERN presentation where they
> > use a 2x replication with NVME for a hyperconverged/HPC/CephFS
> > solution.
> >
>
> Don't do this if you care about your data. NVMe isn't anything better or
> worse than SSDs. It's actually still an SSD, but we swapped the SATA/SAS
> controller for NVMe, but it's still flash.
>
> > I would like to hear some opinions on whether this is really a good
> > idea for production. Is this setup (NVME/2x replication) really only
> > meant to be used for data that is backed up and/or can be lost without
> > causing a catastrophe.
> >
>
> Yes.
>
> You can still loose data due to a single drive failure or OSD crash.
> Let's say you have an OSD/host down for maintenance or due to a network
> outage. The OSD's device isn't lost, but it's unavailable.
>
> While that happens you loose another OSD, but this time you actually
> loose the device due to a failure.
>
> Now you've lost data. Although you *think* you still have another OSD
> which is in a healthy state. If you boot the OSD you'll find out it's
> outdated because writes happened to the OSD you just lost.
>
> Result = data loss
>
> 2x replication is a bad thing in production if you care about your data.
>
> Wido
>
> > Thanks,
> > Frank
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