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EVA6000: mount and unmount-times when (un-)presenting vdisk

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Rudolf Stark
Advisor

EVA6000: mount and unmount-times when (un-)presenting vdisk

Hello,

for Dataexchange we have scripted via RSM (with hostagent) the presentation and unpresentation of a vdisk from one Windows-Server 2003 to another. The script is waiting for the confirmation that the disk is mount (or unmounted) before proceeding.

Is there a way, that the server is not detecting, that a vdisk is unpresented, or represented. So that immediatly after the (re-)presentation to the host, the volume is accessible (without remounting) and writeable.

Thanks and regrads
Rudolf
8 REPLIES
Uwe Zessin
Honored Contributor
Solution

Re: EVA6000: mount and unmount-times when (un-)presenting vdisk

Again, that is not a good idea.

The OS has cached metadata from the mounted volume. If you re-present it a slightly change volume, it can pick up wrong data or even corrupt the volume itself.
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Phillip Thayer
Esteemed Contributor

Re: EVA6000: mount and unmount-times when (un-)presenting vdisk

No there is not a way to do this in Windows. Other OS'es can do this but not windows. On VMWare you can do this and initiate a rescan of the disk volumes. On OpenVMS you can force a mount verification that will force the disk to go through the operations it would normally do on a mount. Windows doesn't have this so if you were to do this it would cause the file system to be corrupted and you could possibly not know it for a long time.

Phil
Once it's in production it's all bugs after that.
Uwe Zessin
Honored Contributor

Re: EVA6000: mount and unmount-times when (un-)presenting vdisk

No, OpenVMS cannot do it either, because if you re-present the disk, the old 'mount-time' in the SCB will show up and OpenVMS will treat it as a different volume (rightly, because it is!).

You DO need to re-mount or use a clustered file system (e.g. the clustered gateway from HP).
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Tom O'Toole
Respected Contributor

Re: EVA6000: mount and unmount-times when (un-)presenting vdisk

I guess you could do it with vms is the intervening mount was readonly, and if mvtimeout was not exceeded. Not sure of the wisdom for doing so, other than to avoid requiring a snapshot license.
Can you imagine if we used PCs to manage our enterprise systems? ... oops.
Uwe Zessin
Honored Contributor

Re: EVA6000: mount and unmount-times when (un-)presenting vdisk

I don't think that is 100% perfect, because VMS will still cache metadata. We tried something like this 20+ years ago (using dual-ported massbus disks) AND mounted with /NOCACHE, but from time to time we still had to remount.


I forgot:
> On VMWare you can do this and initiate a rescan of the disk volumes.

VMFS is a shared filesystem and uses no caching. Metadata changes are serialized using SCSI reservations. You cannot really compare it with NTFS or ODS.
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Phillip Thayer
Esteemed Contributor

Re: EVA6000: mount and unmount-times when (un-)presenting vdisk

OpenVMS will not see it as a different volume from the EVA because you would use the OS Unit ID in Command View to maintain the volume identification. It will go into a mount verification and then return after LUN is presented again (using the same OS Unit ID).

As for Windows, I cannot think of any type of clustered file system that could be used. You would be best served to use snapshots, clones or mirrors and present it to the Windows system as a new disk each time using SSSU to automate the process.

Phil
Once it's in production it's all bugs after that.
Uwe Zessin
Honored Contributor

Re: EVA6000: mount and unmount-times when (un-)presenting vdisk

> As for Windows, I cannot think of any type of clustered file system that could be used.

The Polyserve Filesystem (PSFS) is designed for shared read/write access from multiple Windows servers.
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Rudolf Stark
Advisor

Re: EVA6000: mount and unmount-times when (un-)presenting vdisk

Thank you all for your replies,

I will try some experiments with mirrorclones and polyserve.

Regards
Rudolf