[libvirt-users] Windows Guest I/O performance issues (already using virtio)

[Gionatan Danti]

Il 08-08-2018 19:35 Matt Schumacher ha scritto:
> I’m using ZVOLs to back the VM, and I’m
> using 4k block sizes, which seems to offer the best 4k random
> read/write performance (mail and database workloads), but maybe I’m
> missing something at this layer too.

For the ZFS part: try increasing your volblocksize to 64/128K. While 4K 
volblocksize seems tempting (ie: no read-modify-write, no wasted storage 
bandwidth, etc) it suffers from both a) high metadata overhead and b) 
ineffective compression (which you should *always* enable, using lz4).

Try also disabling sync via sync=disabled. If VM I/O performance get a 
noticeable boost, it means you should use a fast SLOG for ZIL.

Finally, simply realize that Win10/2016 are very, *very* I/O heavy. I 
often wonder on how Microsoft could release something so much I/O 
starved...

That said, when running your virtual machine entirely on an Optane drive 
I would not expect slow I/O at all.
Regards.

-- 
Danti Gionatan
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