On Fri, Jun 26, 2015 at 4:47 AM, Steve Clark <sclark@xxxxxxxxxxxxx> wrote:
> On 06/25/2015 06:44 PM, Chris Murphy wrote:
>> I did a bunch of testing of Raw, qcow2, and LV backed VM storage circa
>> Fedora 19/20 and found very little difference. What mattered most was
>> the (libvirt) cache setting, accessible by virsh edit the xml config
>> or virt-manager through the GUI. There have been a lot of
>
> Which setting did you find most effective?
In terms of performance, unsafe. Overall, it's hard to say because
it's so configuration and use case specific. In my case, I do lots of
Fedora installs, and Btrfs related testing, and the data I care about
is safeguarded other ways. So I care mainly about VM performance, and
therefore use unsafe. I haven't yet lost data in a way attributable to
that setting (top on the list is user error, overwhelmingly, haha).
You might find this useful:
https://rwmj.wordpress.com/2013/09/02/new-in-libguestfs-allow-cache-mode-to-be-selected/
And this:
https://github.com/libguestfs/libguestfs/commit/749e947bb0103f19feda0f29b6cbbf3cbfa350da
Of particular annoyance to me in Virt-Manager is the prolific use of
the word "Default" which doesn't tell you diddly. The problem is
Virt-Manager supports different hypervisors and all of them can have
different defaults which don't necessarily propagate through to
libvirt and I'm not sure that libvirt is even able to be aware of all
of them. So we get this useless placeholder called default. Default is
not good just because you don't know what it is. It's not necessarily
true that default translates into what's recommended - that may be
true, but it may also not be ideal for your use case.
--
Chris Murphy
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