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From Dag Sonstebo <Dag.Sonst...@shapeblue.com>
Subject Re: Live migration causing VM's file system read-only
Date Thu, 19 May 2016 11:10:38 GMT
Hi Lv,

glad you got it sorted. Apologies - I missed your previous post - but DB servers are where
you typically see these problems first since they tend to be I/O intensive. 
You are right in that shared storage allows for live migration between hypervisor hosts without
the underlying disks migrating, however all running VMs will consume bandwidth on your backend
network - and ultimately if there isn't enough network bandwidth or speed between the hypervisor
and the NFS host your VMs will suffer. Typically Linux VMs deal with this better than Windows
VMs, which tend to have a shorter disk timeout period before the disk goes read-only.

For reference have a look at the following KB articles - these are from VMware but the concept
applies whatever hypervisor you are using:

https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1014
https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1009465

Regards,
Dag Sonstebo







On 19/05/2016, 09:37, "Lv Haijiao" <luhaijiao@gmail.com> wrote:

>The issue seems gone while we migrate a SSD+HDD mixed storage which has
>much better I/O performance than previous NFS one.
>
>Thanks Dag,  your advice is helpful.
>
>2016-05-05 21:55 GMT+08:00 Lv Haijiao <luhaijiao@gmail.com>:
>
>> Hi, Dag
>>
>> Thanks for your hint !
>>
>> We don't have chance to reproduce this on our production platform,  but we
>> notice most of these VMs hitting this issue are DB server.
>>
>> Even that, live migration is supposed to consume less bandwidth as
>> majority of VM data is still on the shared storage, need no replication,
>> except the data in memory.
>>
>> Is it right ? :-)
>>
>> 2016-05-05 18:04 GMT+08:00 Lv Haijiao <luhaijiao@gmail.com>:
>>
>>> Hi,
>>>
>>> Here's our environment,
>>>
>>>
>>>    - ACS 4.7.1
>>>    - Ubuntu 14.04 KVM
>>>    - NFS as shared, primary storage
>>>
>>>
>>> While we do a couple of VMs live migration in sequence from physical
>>> server A to B,  the file system of some VMs goes into 'ready only' status
>>> unless we reboot the VM again.
>>>
>>> No clue why we only hit this issue on some of VMs.
>>>
>>> Any advice or experience sharing is most appreciated !
>>>
>>
>>

Dag.Sonstebo@shapeblue.comĀ 
www.shapeblue.com
53 Chandos Place, Covent Garden, London  WC2N 4HSUK
@shapeblue


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