[Info-vax] New filesystem mentioned

[Dave Froble]

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.

So far, I don't see any problems with such assumptions.

RMS is just data, whether it's internal data, or user data.  It gets 
stored on "disk blocks".

I'd assume (bad habit) that if any file system was implemented on VMS, 
that QIOs would be the method for access.  Now, QIO may need to know 
some new things.

For any file system to be implemented on VMS, it's going to have to work 
as other file systems, else what's the use?  If low level code and all 
new file accessing is required, the usefulness becomes much less.  Might 
as well go back to physical I/O.  The purpose of a file system is to be 
a lower level tool transparent to user code.


-- 
David Froble                       Tel: 724-529-0450
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