Friday, February 23, 2007

ds_transfer might be corrupting your backups

If you are using the ds_transfer function in "hot" mode to create backups from your production VMDS, you run the risk of corrupting your backup files so that they cannot be properly restored. I had originally published a post about this to the sw-gis group in July of last year. Recently I was at a client site where the backup scheme used ds_transfer in "hot" mode and I realized that it would be helpful to repost this information in this blog.

If you are using PowerOn, it is possible that the original implementors set up your backup scheme to use ds_transfer in "hot" mode. You may want to read the following article and see if your backups are in jeopardy.

Original Article follows....

Since there is a discussion about backups and the ds_transfer mechanism was mentioned as a solution I thought I would throw out a warning about that approach. Simply put, when using in "hot" mode, you should ensure that no one is writing to the database while you are performing the ds_transfer.
The typical ds_transfer scenario involves ds_transferring one DS file at a time. Imagine that you ds_transfer gdb.ds and it takes a total of 15 minutes. 10 minutes into the ds_transfer a user writes a fiber(1234) RWO and geometry to that partition. But the alternative that was being written to had already been processed at minute 2 of the 15 minute process. After the 15 minutes are done, the ds_transfer starts working on the rwo.ds file.
You will not see a problem in the live production dataset, but you will now have a situation where the "ds_transferred" dataset has an inconsistency between the rwo.ds and the gdb.ds. This is a simple scenario, but imagine that changes are at a larger scale or possibly involve adding/removing alternatives while a hot ds_transfer is in progress. These will all be permitted actions but may cause unintended results in the "ds_transferred" files. If you are using the with "hot" mode you should try opening a copy of your recently ds-transferred files to see if they are consistent with each other.
If you want to continue using the ds_transfer functionality to perform "hot" backups, refer to ds_transfer.transfer_partition() to see how it might be beneficial to you. This method has the advantage of allowing you to snapshot all DS files in a partition at the same time so you will not encounter any of these data consistency issues.

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