[Info-vax] New filesystem mentioned

[Arne Vajhøj]

On 5/13/2019 8:30 PM, Dave Froble wrote:
> On 5/13/2019 6:53 PM, Arne Vajhøj wrote:
>> On 5/13/2019 5:37 PM, Dave Froble wrote:
>>> On 5/13/2019 2:36 PM, Michael Moroney wrote:
>>>> Simon Clubley <clubley at remove_me.eisner.decus.org-Earth.UFP> writes:
>>>>> There's a reason (multiple reasons actually) why so many operating
>>>>> systems now support ZFS.
>>>>
>>>>> Unfortunately, VMS isn't likely to be one of them, given the lack
>>>>> of support in VMS for modular plugin filesystems. That means adding
>>>>> ZFS to VMS would be a major job.
>>>>
>>>> If I recall, A mentioned that ZFS and other file systems lacked the
>>>> cluster support
>>>> needed for clusterwide operation that VMS needs, and would require
>>>> mega rototilling
>>>> to add it. I don't know the details.
>>>>
>>>
>>> An interesting statement.
>>>
>>> I'm wondering what would be required in the filesystem to support VMS
>>> clustering?
>>>
>>> Not that I'm an expert on VMS clusters, but it has been my impression
>>> that the OS did all the work.  But what do I know?
>>
>> The answer must depend a lot on what is meant by "file system".
>>
>> I do not think there is anything in the on disk bytes that
>> are relevant for clustering.
>>
>> The code that does the physical transfer of data between
>> disk and memory should not have anything relevant for
>> clustering.
>>
>> But there are some higher level code that need cluster
>> awareness. At least code that checks if a file being
>> opened is already in use on another node. And much more
>> to support effective locking of records and byte ranges
>> in cluster environment.
> 
> The DLM is cluster aware, and any locks are respected over the entire 
> cluster.
> 
> For file system locks, the top level locks might be on the filespec, 
> which includes device.  As I may have mentioned, I'm not very 
> knowledgeable about VMS clusters.  Someone who knows more can add some 
> details.  I believe every "disk" in a cluster has a unique name.  So the 
> resource lock on that device and filespec should be respected and unique 
> throughout the entire cluster.
> 
> The sublocks are for record numbers in the file, and would be respected 
> throughout the cluster.
> 
> I believe it's just that simple.
> 
> Now, the "stuff" that makes the DLM work across the VMS cluster, that 
> may be rather complex, but, it's already in there.  There are things 
> such as moving the locks to the node with the most usage, and such. 
> Really a nice tool, and from the early 1980s.  I used it for my database 
> product developed in 1984.  Still working.

Yes.

But now you are assuming that ZFS is just an ODS-something format and
that RMS, SYS$QIO(W) etc. just runs on top of it.

Arne