Introduction

Taking StoreOnce as an example of a Backup to Disk device, there are mainly 3 types of stores possible: NAS, VTL and Catalyst. Other brands have similar types. In general, all of these types will deduplicate data which means it will not always be easy to predict the disk usage change when new data is stored or when data is deleted. That is something to keep in mind for any type of store.

From a Data Protector point of view, a NAS share would be used for a file library, a VTL would behave as a physical tape library and a catalyst store would be used with a DP B2D device. The way disk space is used and especially the way data is removed will be different for all 3 types.

File Library on a NAS share

On a File Library, file depots will get removed at the beginning of a session when they have expired. So basically when the session starts, the library will be checked for expired depots and they will get deleted. Note that as for any store type, deletion of the file depots does not tell us anything about how much space will be regained.

VTL

A VTL or Virtual Tape Library in Data Protector will behave as a physical tape library. That also means that data will only be deleted when the (virtual) tape is overwritten. So even when only 10% (as an example) of the tapes has protected data on it, all the data of all tapes will be kept on the store, even when unprotected. This is exactly the same as with physical tape media. This also means that the number of virtual tapes should be limitted to a number appropriate to fit all the contained data on the available disk space. When the store is running out of space, a short term solution may be to format some expired tapes (as that would get the data deleted). But on the longer term that is not the solution as the newly formatted tapes will fill up again and the same issue will re-appear. So the only good solution will be to either add disk space or remove some tapes from the library.

Catalyst Store

For a DP B2D device on a Catalyst store (or similar on other brands) the story of data deletion will again be different. For these devices there will be a regular maintenance cycle (once per day by default; can be changed in the global file) where expired media will get deleted. When media get deleted on the DP side (media dissapear from the pool and IDB) a command will be sent to the B2D device to delete the corresponding object from the store. Note again this won't tell us anything about the possible disk space gain as data is deduplicated and chunks may still be linked to other objects on the store.

Summary

As we can see cleanup on a Catalyst store will happen at a regular pace: once a day by default. On a VTL, the data will only get removed when a virtual medium is overwritten (or the medium is manually formatted or deleted). And on a NAS share, in case of a DP File Library, data will get deleted at the start of a next session when the data is expired at that time.

You may be interested to some of my other Support Tips too: Support Tips listed per category.