[Info-vax] Wide area cluster, metro area network, seeking info

[Marc Van Dyck]

Rich Jordan laid this down on his screen :
> On Tuesday, June 15, 2021 at 12:55:10 PM UTC-5, Michael Moroney wrote:
>> On 6/15/2021 9:24 AM, Arne Vajhøj wrote: 
>>> On 6/11/2021 2:20 PM, Rich Jordan wrote: 
>>>> On Thursday, June 10, 2021 at 10:22:58 AM UTC-5, Marc Van Dyck wrote: 
>>>>> Rich Jordan was thinking very hard : 
>>>>>> We are looking at the possibility of putting VMS boxes in two 
>>>>>> locations, with 
>>>>>> Integrity boxes running VSI VMS. This is the very beginning of the 
>>>>>> research 
>>>>>> on the possibility of clustering those two servers instead of just 
>>>>>> having 
>>>>>> them networked. Probably have to be master/slave since only two 
>>>>>> nodes and no 
>>>>>> shared storage. 
>>>>>> 
>>>>>> After reviewing the various cluster docs, they seem to be focused on 
>>>>>> older 
>>>>>> technologies like SoNET and DS3 using FDDI bridges (which would 
>>>>>> allow shared 
>>>>>> storage). The prospect has a metropolitan area network but I do not 
>>>>>> have any 
>>>>>> specs on that as yet. 
>>>>>> 
>>>>>> Are there available docs relevant to running a distributed VMS 
>>>>>> cluster over a 
>>>>>> metro area network or fast/big enough VPN tunnel? Or is that just the 
>>>>>> straight cluster over IP configuration in the docs (which we've 
>>>>>> never used) 
>>>>>> that we need to concentrate on?  
>>>>> Before going into the technical details, wouldn't it be interersting to 
>>>>> know what you want to achieve, and discuss whether clustering is the 
>>>>> best way to achieve it ? I, for one, would be interested to know why 
>>>>> you 
>>>>> believe that clustering without shared storage can be more beneficial 
>>>>> than simple networking. 
>>> 
>>>> The point: the system at the second location will be a backup site 
>>>> and/or disaster recovery box. There is no third location and I have 
>>>> no info on the likelihood of getting one. 
>>> If the business problem is to ensure that the second location always 
>>> have a copy of all data, then a VMS cluster may not be the optimal 
>>> solution. 
>>> 
>>> There are other VMS features/products than clustering that could 
>>> be relevant.
>> It appears to me one possibility is fiberchannel presenting RAID-1 
>> units, with one member of each RAID-1 at the main site and one at the 
>> backup site connected with dark fiber (FOIP?). VMS system (no cluster) 
>> at main site and either no system or a cold backup at the backup site.
>
> I love the discussions that questions like this bring up.
>
> More info.  The base requirement is to have a backup system at an existing 
> remote office; this backup system will be kept 'up to date' and available for 
> use if the primary site or system fails.
>
> One option is nightly backup/restore operations, so (up to) one day latency.  
> This is considered the low end of acceptable.  The customer asked about 
> options for keeping the backup closer to current.
>
> The system cannot be quiesced during production hours (about 11 hours per day 
> weekdays) so we cannot run periodic backups during those hours.  Programs 
> just were not written that way.
>
> Since we can't do intraday backups, one option is shadowing, and so 
> clustering.  I didn't mention HBVS (my bad) but its the reason for the 
> cluster option.  I was mainly looking for info about running a cluster over a 
> WAN connection/metro area network in case anyone had that experience, since 
> much of the documentation available is pretty old and seems to concentrate on 
> using FDDI bridges over what are currently modest speed links.  
>
> VSI _is_ involved and we are working with them on this possibility.  At this 
> point I think the additional license subscription costs are going to kill the 
> HBVS/cluster option, especially if a third node was needed (and a third 
> location and connection, and set of licenses).  That means going with the 
> one-day latency backup option and generating and testing the procedures for 
> failing back to the main system when it is available again.
>
> We have not determined availability of dark fiber; the intention is to use 
> the metro area network, and so cluster over IP.  We did some price checks on 
> the equipment needed to bridge the sites and  I am told it is not within the 
> budget.   
>
> Thanks
>
> Rich

You don't really need clusters, HBVS, and dark fiber for that. You can
have controller-based storage replication between the two sites, 
running
on fibre channel over IP. And just a cold system on the backup site 
that
you can boot if the primary site fails. What I don't know is the price
aspect, i.e. whether there are reasonably cheap storage solutions for
controller-based replication and FC/IP.

-- 
Marc Van Dyck