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

[Alexandre DERUMIER]

>>What is your vm guest os ? kernel version ?
>>
>>Guest OS can be Windows (any) and Linux (any version).

I ask the question because old windows virtio driver don't send flush correctly,

and some linux kernel too (it's really safe since 2.6.32 - 2.6.33 if I remember, depend of filesystem, virtio driver -lvm-mdadm-dm version ..)
http://monolight.cc/2011/06/barriers-caches-filesystems/

>>2. It is often happen to Linux VM swap space. 
mmm,good point, I don't known how flush is working with swap.



----- Mail original ----- 

De: "Stanislav German-Evtushenko" <ginermail at gmail.com> 
À: "Alexandre DERUMIER" <aderumier at odiso.com> 
Cc: pve-devel at pve.proxmox.com, "Dietmar Maurer" <dietmar at proxmox.com> 
Envoyé: Mardi 18 Novembre 2014 17:58:31 
Objet: Re: [pve-devel] Default cache mode for VM hard drives 





Alexandre, 

This is actually so long story I was investigating more then a year until got this working without out-of-sync. Two Domain Controllers died because of this. We'd been trying to replace most of hardware/firmware/disabling TOS/etc but the issue had never gone. 



What is your vm guest os ? kernel version ? 



Guest OS can be Windows (any) and Linux (any version). 

1. It happens not often for Windows VM but when happen can be fatal. 

2. It is often happen to Linux VM swap space. 

3. It doesn't usually happen to Linux VM ext4 with barriers enabled and I've seen this only happen to Linux VM ext4 with graylog2 installed on it (java application). I don't know why, may be this application can ignore barriers somehow. I don't understand this. 


<blockquote>
do you have disabled barrier in /etc/fstab ? 

</blockquote>

Never disabled. 


<blockquote>
What is your host storage ? (soft|hard raid ?) 

</blockquote>
Hardware RAID 



Best regards, 

Stanislav