[Info-vax] New filesystem mentioned

[Arne Vajhøj]

On 5/13/2019 8:52 PM, Arne Vajhøj wrote:
> 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.

https://en.wikipedia.org/wiki/ZFS#ZFS_compared_to_other_file_systems

https://en.wikipedia.org/wiki/ZFS#Summary_of_key_differentiating_features

Arne