Re: volume shadowing over LAVC ?

Richard B. Gilbert wrote:
Check out what it costs before you get all excited about it!

There are licences that cover shadowing, as opposed to just disk by disk.

Also, since volume shadowing is software based, you place additional CPU load on your cluster. Then there is the network load.

Yes. But sometimes, the ethernet is all you have and you can't afford to have other links between the 2 nodes=, at which point host based shadowing becomes a good solution.

When a cluster member crashes, the shadowset has to be checked for consistancy, block by block.

Nop. It is when the crashed node that comes back on line and wants to re-integrate its disks that the rebuilding has to take place. And there are now parameters to control how much cpu/bandwidth is used to do this.



I've run both host based volume shadowing and HSZ40 or HSZ50 based hardware RAID and believe me, hardware is better!!!

Hardware shadowing that is totally separate of VMS can be dangerous depending on configuration with regards to cluster partitioning. With host based shadowing, your disks are "part of the cluster" and benefit from the cluster partitioning safeguards. And VMS has flags in each disk to indicate which disk is the most recent. So, if you remount yor shadowset, it knows which disk in teh shadow set has the most recent data to be used as source of data to update the other disks.

With hardware systems, you don't have that extra logic that is part of VMS.
.

Relevant Pages

  • Re: Error message question: The physical disk cannot...
    ... for the internal disks and one for the shared disks. ... >I received the following message today when configuring Cluster ... > storage bus as the boot disk. ... > 1) Is this a hardware issue that can only be resolved by new hardware ...
    (microsoft.public.windows.server.clustering)
  • Re: Blue Screen on 2 nodes - Please Help
    ... The Disks are what are known as VDisks - they are created on a HP EVA 5000 ... With regards to the resources taking 5mins, it does seem excessive, ... Either a bad driver or hardware is always the cause. ... is, the cluster has not been right for sometime, and I am unable to narrow ...
    (microsoft.public.windows.server.clustering)
  • Re: Cluster Disaster Recovery with standby cluster in second Site
    ... File cluster and serves files from shared Disks. ... The hardware in Site 2 has access to the replcated SAN Disks and is ...
    (microsoft.public.windows.server.clustering)
  • Re: volume shadowing over LAVC ?
    ... There are licences that cover shadowing, as opposed to just disk by disk. ... hardware RAID and believe me, ... Hardware shadowing that is totally separate of VMS can be dangerous depending on configuration with regards to cluster partitioning. ...
    (comp.os.vms)
  • Re: Clustering Problem
    ... >> Didn't you have to change the allocation class of the disks? ... > node name) and if shadowing is used (this puzzled me for a while, ... > Since disk names have to be unique within the cluster, do all your disks ... Our cluster is connected to a HSZ80-Controller, ...
    (comp.os.vms)