[ClusterLabs] Antw: Re: Question on sharing data with DRDB

Digimer lists at alteeve.ca
Thu Mar 21 11:18:18 EDT 2019

On 2019-03-21 2:53 a.m., Ulrich Windl wrote:
>>>> Digimer <lists at alteeve.ca> schrieb am 20.03.2019 um 17:37 in Nachricht
> <37a2b613-62ce-a552-804a-df5199674b00 at alteeve.ca>:
>> Note;
>>   Cluster filesystems are amazing if you need them, and to be avoided if
>> at all possible. The overhead from the cluster locking hurts performance
>> quite a lot, and adds a non-trivial layer of complexity.
> Yes, that's the true challenge. It's sad that NFS might provide better
> performance than a cluster filesystem will.

There's nothing sad about it. Shared filesystems like NFS and cluster
file systems like GFS2 are designed to solve different problems.

>>   I say this as someone who has used dual-primary DRBD with GFS2 for
>> many years.
>>   To expand on why you can't use something like ext4; Non-cluster-aware
>> file systems expect all changes to the backing device to go through it.
>> So there's no mechanism to tell the FS on one node that blocks have
>> changed because of actions on another node. Likewise, they have no
>> mechanism to coordinate sane and safe access to blocks. These mechanisms
>> are exactly what makes a cluster FS what it is.
>> digimer
>> On 2019-03-20 11:52 a.m., Emmanuel Gelati wrote:
>>> If you need to access from both nodes, you need to use primary/primary
>>> mode in drbd
>>> Il giorno mer 20 mar 2019 alle ore 16:51 JCA <1.41421 at gmail.com 
>>> <mailto:1.41421 at gmail.com>> ha scritto:
>>>     OK, thanks. Yet another thing I was not aware of in the clustering
>>>     world :-(
>>>     On Wed, Mar 20, 2019 at 9:41 AM Valentin Vidic
>>>     <Valentin.Vidic at carnet.hr <mailto:Valentin.Vidic at carnet.hr>> wrote:
>>>         On Wed, Mar 20, 2019 at 09:36:58AM -0600, JCA wrote:
>>>         >      # pcs -f fs_cfg resource create TestFS Filesystem
>>>         device="/dev/drbd1"
>>>         > directory="/tmp/Testing"
>>>         >         fstype="ext4"
>>>         ext4 can only be mounted on one node at a time. If you need to
>>>         access
>>>         files on both nodes at the same time than a cluster filesystem
>>>         should
>>>         be used (GFS2, OCFS2).

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