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Continuos Access. How to Access Destination Vdisks


Continuos Access. How to Access Destination Vdisks


I have two EVA4100 replicating with CA, through two FCIP gateways.

Everything working just fine!!

I would like to access replicated Vdisks on the destination site. I know i can snapshot destination Vdisks and present them to hosts, but i would like to access the replicated Vdisks directly.

I know there is an option to access in Read Only mode. I tried this option, but i noticed that while the disk is presented to a host in the destination site, changes made in the original Vdisk are not visible in the replicated copy. I have to unpresent, re-present it, and then i can see the replicated changes.

Is this correct? I would like to see continuously the changes made in original Vdisk. I have no need to have write access, but i would like to see the changes.

Is this possible?

I hope i explained myself!

Thanks in advance!
Uwe Zessin
Honored Contributor

Re: Continuos Access. How to Access Destination Vdisks

Not possible, because the file system you are using (NTFS? ext2/3?) does not know how to deal with such a situation. And the server on the destination side does not get notified of meta-data changes anyway, because the filesystem on the source also does not know how to send updates.

Even with R/O access it is dangerous to access a living filesystem, because the meta-data is not stable. In the worst case your file system handler or even the whole operating system can crash, because it sees inconsistencies.
Honored Contributor

Re: Continuos Access. How to Access Destination Vdisks


How are you trying to access the data on the Vdisks ? is it a filesystem that you are trying to mount as readonly and then see the data.
If yes, then what you observe is what will happen. This is what I feel/understand about what happens.
When you read only mount the filesystem on the destination, the OS keeps a copy of the metadata of the filesystem in memory/kernel (This is the state of the filesystem as of time when you mount it).
Now there are changes happening at the primary side which are being replicated to the destination via CA. These updates are at storage level and the OS at the destination does not know anything about this and hence its memory/kernel copy of filesystem state (having details of files/dirs as of when the filesystem was read only mounted) and the actual state differ.
Thus at this point if you unmount the filesystem and then mount it as read only again on the destination - the latest state of filesystem metadata is checked and maintained in the memory/kernel and thus you see the changes being reflected only after remounting the filesystem.

Is this what you are looking for ?


Re: Continuos Access. How to Access Destination Vdisks

Thanks for such fast answers!

Well, you both explained the situation clearly. And i think i understood that what i wanted is not possible. Thanks for the confirmation.

I didnt mention my hosts are Windows, and NTFS partitions.

Let me push you a little bit further. Is what i mentioned posssible with any other product in the market?

Thanks a lot, you both were very helpful

Ivan Ferreira
Honored Contributor

Re: Continuos Access. How to Access Destination Vdisks

With XP storages and other (Hitachi) similar, you can temporarily "split" your remote copy and access in read only or read write mode. You can "resync" again later. But as Uwe said, there are metadata information that you should access that a read only disk won't give you accurate information.
Por que hacerlo dificil si es posible hacerlo facil? - Why do it the hard way, when you can do it the easy way?