What Happens when BC LUNS are overwritten

[gstonian]

Hi,

We have Business Copy and regularly do snapshots of Luns which host an Oracle Database. This is to provide a quick copy of the DB for testing etc.

My question is what happens when the DBA's use area presented by the BC Snapshot LUNs and overwrite the data with a completely seperate tape restore ?

Does the snapshot lun just become a normal lun or does Business Copy keep working ? I know the data isn't overwritten by Business copy but will it keep trying to check or copy the data when the original is changed ?

Thanks

[Uwe Zessin · Accepted solution]

I guess you are talking about an EVA storage array?

No, the snapshot will not turn into an original virtual disk. If you overwrite all blocks, it will implicitly turn into a fully-allocated snapshot - that means it will occupy the same amount of storage like the original disk.

BC will keep working, provided that is enough free space in the disk group to allocate enough for the snapshot.

If you want to turn a snapshot into an original virtual disk... the only possibility I know is to give up the data in the original space and start a 'restore from snapshot' on the EVA. That is only possible in very recent versions of XCS.

[gstonian]

Thanks.

I knew the snapshot would still be a snapshot LUN - I just wanted to check that by overwriting the data on this presented BC Lun, Business Copy wasn't going to keep trying to copy blocks over to it when the source blocks were changed.

Thanks

[Sheldon Smith]

As I have always understood it, the EVA does not care from where the change comes. As a modification comes to an unchanged PSEG, the PSEG is replicated, the pointers are split and the IO completes. From that point on, that area is simply separate PSEGs, each in its own vdisk or snapshot structure.

[gstonian]

Thanks for the above answers