> What do you mean by "small block sizes"?

inside a VM, or directly on the mounted glusterfs;
dd if=/dev/zero of=tmpfile  bs=1M count=100 oflag=direct
of course, a terrible way to write data, but also things like compiling 
software inside one of the VMs was terrible slow, 5-10x slower than hardware, 
consisting of almost only idling.

Uploading disk images never got above 30MB/s. 
(and I did try all options i could find; using upload_disk.py on one of the 
hosts, even through a unix socket or with -d option, tweaking buffer size, all 
of which made no difference).
Adding an NFS volume and uploading to it I reach +200MB/s.

I tried tuning a few parameters on glusterfs but saw no improvements until I 
got to network.remote-dio, which made everything listed above really fast.

> Note that network.remote-dio is not the recommended configuration
> for ovirt, in particular if on hyperconverge setup when it can be harmful
> by delaying sanlock I/O.
> 
> https://github.com/oVirt/ovirt-site/blob/4a9b28aac48870343c5ea4d1e83a63c1...
> (Patch in discussion)

Oh, I had seen this page, thanks. Is "remote-dio=enabled" harmful as in things 
breaking, or just worse performance?
I was a bit reluctant to turn it on, but after seeing it was part of the virt 
group I thought it must have been safe.
Perhaps some of the other options like "performance.strict-o-direct on" would 
solve my performance issues in a nicer way (I will test it out first thing on 
monday)

Thanks (I'm not much of a filesystem guy, thanks for putting up with my 
ignorance)
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