A user posted this as a response to “The Many flavors of EMC TimeFinder“Â I felt it rated it’s own post.
Q: “My experience is mostly using IBM Sharks. Iâ€™m now working in a very large EMC environment, foucsed on backup. Iâ€™m wondering if the TimeFinder/Cloneâ€™s cloned volume can be permanently mounted on another host. Specifically, I want to avoid importing a nd exporting DGs from Veritas every time I need to â€™splitâ€™ the mirror, as I would have to do with TineFinderâ€™/Mirror. “
A: TimeFinder/Clone can in fact be a permanent copy of the data.Â As long as the either of the copy options are set, the -precopy option, which copies all data before the session is activated, or the -copy option, which performs a full background copy of the data while the target (clone) device is available to the backup/development host, is used.
The default, (no switches used) will not result in a full clone and as such is only available while the clone session is in the “Active” state.
Q: What Iâ€™m looking for a is a point in time copy which is mounted on a backup media server while the production data disk are mounted on the production server. The application on the production server would be paused, then the clone would happen, then the application could be restarted. The cloned data would â€œmagicallyâ€ appear on the clone volume set mounted on the backup media server.
A: If you’re doing this simply for backup, then copy-on-access is easier and more flexible.Â COA allows you to create and activate a session, copy the data, and terminate it immediately.Â Truthfully TimeFinder/SNAP is equally up to this task (as it’s largely the same thing) but in my opinion you get more flexibility by purchasing clone instead of snap, though you do spend more money on disks in the process.
Unfortunately, as I’m assuming you’re talking about a Windows environment, there isn’t much “Magical” about it.Â
Q: The largest issue Iâ€™ve run into is the insistence by a few EMC folks that the clone volume must be mounted on the prod host, then unmounted and mounted on the backup host.
A: Again, assuming you’re talking about Windows, this is incorrect.Â You can’t remount the snap or clone of a production volume back to the same host because windows is largely dependant on the Signature of the drive.Â Doing so can actually confuse windows into thinking that there are two copies of the disk and cause data corruption.Â (I can’t say anything, the same is true of AIX, which, if you’re using LVM and not raw disks, has the same signature (they call it PVID) dependency.)
I’ve worked in several environments where the target volumes are simply unmounted, synched, and remounted.Â So long as the target ID and the signature don’t change, this is not usually an issue.
The benefit to using clone is that you can leave the session active, or use one of the ‘copy’ options to produce a full copy.Â Then, restoring from the disk in the case of a failure becomes a real option.Â You simply reverse the sync, remount the production volumes, and start the application or database from there.Â (Ok, it’s not simple, but I’m not sure even I have the drive space to post the full procedure here.Â 🙂 )