[DRBD-user] drbd 8.4.7 out-of-sync on disabled host page cache in VM

[Armin Schindler]

On 20.04.2019 14:38, acs at sysgo.com wrote:
>> On 13 March 2019 at 11:47 Roland Kammerer <roland.kammerer at linbit.com> wrote:
>>
>>
>> On Tue, Mar 12, 2019 at 09:08:42AM +0100, Armin Schindler wrote:
>>> On 3/11/19 1:42 PM, Roland Kammerer wrote:
>>>> On Mon, Mar 11, 2019 at 11:13:11AM +0100, Armin Schindler wrote:
>>>>> 2 hosts Debian 9 (stretch) with default DRBD version 8.4.7.
>>>>
>>>> Please retry with the current 8.4.11 version of DRBD. You can it from
>>>> here:
>>>> https://www.linbit.com/en/drbd-community/drbd-download/
>>>
>>> Okay, thanks. I will test 8.4.11.
>>>
>>> Do I need to change/update the tools as well or just the kernel driver?
>>> I currently use drbd-utils 8.9.10.
>>
>> They should be fine. I don't remember any non-corner cases fixes for 8.4
>> in drbd-utils.
> 
> I tried version 8.4.11 and the problem persists.
> When using Qemu/KVM virtio disk with a caching mode that uses host page cache,
> or when using just a filesystem like ext4 on (without Qemu/KVM) on the host, the
> drbd device gets out of sync after a while.

To correct my statement above, the out-of-sync happens when using
KVM/Qemu with a cache mode that is NOT using page cache (like option
"none"). When using option like "writethrough" which uses host page
cache, no out-of-sync happens.
When using the drbd device as mounted-on-host with e.g. ext4,
out-of-sync happens as well.

Armin

> The drbd device is on top of a LVM-lv on both nodes.
> 
> Is there anything else I can test?
> According to some (old) posts, this is a known issue for a long time now. But I never
> found any resolution or fix.
> 
> Thanks.
> Armin

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