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516
September 8th, 2008 06:00
Easy question about Replication manager regarding snaps vs clones
Ok, total EMC dummy here. I just need to know, a snap that is mounted without the read-only checkbox, it is writeable, but does that write back to the original? I want it to be writeable, but after the replica expires after 6 days, I want that data to go away. I just need a SQL instance that people can run reports off of, without hammering production.
Read-only is truly read-only, what does unchecking that mean to me, for a snap? I am guessing it works the way I expect, since a clone would allow write back to the original, but I just can't find a clear answer anywhere in the manuals, and I can't take a chance.
Read-only is truly read-only, what does unchecking that mean to me, for a snap? I am guessing it works the way I expect, since a clone would allow write back to the original, but I just can't find a clear answer anywhere in the manuals, and I can't take a chance.
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JamesBEMC
257 Posts
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September 8th, 2008 07:00
Ok, correct, when you write to a "snap", then the data does not get written back to the production aka source volume/LUN.
Now, the term "snap" has many meaning, depending on the context.
In the case of "snap", we'll talk on a storage level.
Clariion has 2 ways of replicating a source volume/LUN.
Snapshot aka snap - fast to create
a point in time representation of the source volume with copy on first write to protect that "time view".
All reads come from the source volume and any writes to the source means the original blocks must FIRST be copied to the snapshot "LUN".
This does have performance impact to the source LUN.
Clone - needs initial or incremental syncronization
a full standalone copy of your source - the initial potential source volume performance impact is only at sync time. If you do this during a quiet period, production impact will be at worst minimal but probably nothing at all.
As soon as the sync is done, the clone is fractured off from the source and as long as the clone and source are not using the same physical drives on the backend (planned right, they wont be) - you can do anything to the clone and the production lun will not be performance impacted or written to.
That "Read-only" tick-box actually means the volume (be it a snap or clone) will be mounted to the mount host as a read-only volume to Windows. Really, it means we will not unset the VSS Shadow readonly flag.
Hope it helps
James.
Cheers
James.
texrob
8 Posts
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September 8th, 2008 08:00