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

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.

Danti Gionatan
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