[Bugs] [Bug 1375431] [RFE] enable sharding and strict-o-direct with virt profile - /var/lib/glusterd /groups/virt

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1375431

Krutika Dhananjay <kdhananj at redhat.com> changed:

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--- Comment #9 from Krutika Dhananjay <kdhananj at redhat.com> ---
(In reply to Pranith Kumar K from comment #8)
> (In reply to Krutika Dhananjay from comment #7)
> > (In reply to Pranith Kumar K from comment #6)
> > > (In reply to Krutika Dhananjay from comment #5)
> > > > (In reply to Pranith Kumar K from comment #4)
> > > > > (In reply to Krutika Dhananjay from comment #3)
> > > > > > (In reply to SATHEESARAN from comment #1)
> > > > > > > strict-o-direct also needs to be turned on and remote-dio to be turned off
> > > > > > > 
> > > > > > > In total there are 4 options :
> > > > > > > 
> > > > > > > features.shard=on
> > > > > > > cluster.data-self-heal-algorithm=full
> > > > > > > performance.strict-o-direct=on
> > > > > > > network.remote-dio=disable
> > > > > > 
> > > > > > Just for the record, the option features.shard=on and
> > > > > > cluster.data-self-heal-algorithm=full will be added to group virt. O-DIRECT
> > > > > > options will be skipped since not all users might want to use cache=none
> > > > > > qemu option, and so it is best to configure them separately.
> > > > > > -Krutika
> > > > > 
> > > > > odirect options honour the o-direct flag for open. Does qemu always open
> > > > > with o-direct even when cache is not set as 'none'?
> > > > 
> > > > When cache=none is not used, I believe qemu won't be passing O_DIRECT flag.
> > > > Now that I remember, there was one more reason Vijay mentioned about a
> > > > certain ping-timeout issue, which if fixed, we won't need to rely on any of
> > > > the odirect option (even if cache=none is used by qemu).
> > > > 
> > > > -Krutika
> > > 
> > > Okay, so what is the plan for the deployments? Are we going to suggest users
> > > to apply virt-profile and explicitly set remote-dio to off in every
> > > deployment, considering that cache=none is used by default?
> > 
> > cache=none is used by default? Isn't that a very specific case and confined
> > to ovirt users alone?
> 
> It seems like quite a few of them are recommending cache as none for
> different reasons, including proxmox which is a bit popular in gluster-users:
> https://pve.proxmox.com/wiki/Performance_Tweaks#Disk_Cache
> https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/
> html-single/Virtualization_Tuning_and_Optimization_Guide/index.html#sect-
> Virtualization_Tuning_Optimization_Guide-BlockIO-Caching
> 
> So I am thinking it is better to put it in the profile than to suggest users
> to change this for all deployments. It seems to be safer option as well
> because it eliminates human errors where users may forget to turn this
> option off which may lead to VM pauses.

I'm not entirely convinced. What if not all users have the kind of heavy
workload that was used in testing which led to VM pause and required o-direct
options to be enabled? Why should all users suffer performance penalty
associated with having odirect options set?

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