[pve-devel] Default cache mode for VM hard drives

Stanislav German-Evtushenko ginermail at gmail.com
Fri May 29 14:58:54 CEST 2015


On Fri, May 29, 2015 at 3:51 PM, Dietmar Maurer <dietmar at proxmox.com> wrote:
>
>> > Come to think of it, you could probably say inconsistent garbage is
>> > also just garbage.
>> >
>> > Does it _really_ fix the problems if you use a different cache option
>> > in qemu? I'm just asking because it seems weird that a program (or
>> > OS for that matter) is _relying_ on bad data to be, well, not so bad.
>>
>> The issue is reproducible only with cache=none and cache=directsync
>> and it is never reproducible with other cache modes.
>
> So we still not understand the problem 100% :-/
>
> You mention that it only happens on some special guest OS? Did you
> also test different drivers (virtio, ide, scsi)?
>

1) On any guest OS (Linux or Windows) where swap is used actively
2) As I remember I've seen the same issues happening for ext3
partitions on Linux guests (where barriers are off by default) but it
was quite long time ago becase all guest systems are on ext4 now


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