Considerations for Creating Volume Sets
There are several options and parameters provided to the administrator for expanded functionality in how the storage system is used. Write Order can be set to Contiguous (the A and B side of a media is used before using the next media surface) or Staggered (All A side surfaces are used before using the B side surfaces). The Volume Set Type may be set to Fixed, Automatic, or Manual extensibility. Also the administrator is able to determine the maximum size of a volume set.
Because of these changes it is important that from the very beginning you are careful in your consideration for planning the implementation and creation of your volume sets.
For example, happy to get away from single surface limitations, you might decide that it would be best and easiest to simply "virtualize" the whole storage library into one large volume set. With this in mind, you format all of your WORM media surfaces in the library into a single volume set. While this is possible and may be easier for you up front, this may not be advisable. Due to the limitations in the capacity of the storage library itself and the number of surfaces contained in this single volume set, this may create practical management issues later on, once the volume set becomes full and you need to either write new data or move a member surface off-line.
Just as it is inadvisable to write all of your files to the root of the C drive of your server, likewise in most cases it is not advisable to simply create one large volume set, and write all of your files to the root of that volume. Keeping your volume sets logically organized and manageable in size and number is important. Careful planning of this is critical to the long-term practicality of your volume sets.
Start this process by determining the storage needs that you have. This is based on how your data is naturally grouped and accessed. For example, is your data logically divided into groups such as company departments (E.g. Accounting, Sales, Engineering)? Is your data stored based on the month and calendar year? Are you using this as a primary backup target? This forms the basis for the number and types of volume sets you will create.
Next determine how much storage space is required for each group of data. While this may be difficult to determine, you would obviously want allow for sufficient space on a given volume set, so that you do not run out of storage space when adding data to a given volume set that is now full.
You will need to keep in mind the physical media capacity of the storage libraries that you are using as it relates to the size of your volume sets. While InveStore v4 allows you to create a volume set using all of the surfaces in the library, or to create one that spans across more than one library, in general we do not advise that you do this. This is more of a practical management issue. The volume set may become physically too cumbersome especially if you should exceed the capacities of your storage devices.
Along the same lines, your volume sets should be created keeping in mind how you plan to store offline-archived data. Take into account the importance of being able to keep all the members for a single volume set together and properly labeled.
When creating your initial volume sets there are several format options that you will set that define the functioning parameters for your sets.
1) The first option is Write Order. This determines how data is written to the individual member surfaces. A Contiguous write order is where the A and B-side of media is used before using the next media surface. A Staggered write order is where all A side surfaces are used before using the B-side surfaces.
For example, if you are using a storage library that has 4 or more drives you may want to set your volume set to Staggered. This is so that more surface members of a given volume set can be under the read head of the drives in the library at the same time.
Or you may want to set your volume set to Contiguous, so that you keep like-kind data located on surfaces of a group of media in a given volume set, rather than potentially spreading out the data out over surfaces on a large number of media.
2) Consider setting the Number of Surfaces (used to begin the set) to an even number of either 2 or 4 surfaces (depending on the Write Order). The Maximum Number of Surfaces should be set to a value higher than the storage space requirement that you calculated. (You may set all of your volume sets to the maximum capacity of the storage device, even though you will not actually add all of these surfaces to the volume sets. This allows the greatest flexibility for your volume sets to grow as needed.)
Set the Volume Set Type to Automatic or Manual extensibility allowing the set to grow as needed. We suggest starting in this fashion rather than formatting up front all members of the complete set at creation time.
The primary reason for this is that it allows you to manage the process better as you proceed. You may find that you only require 6 surfaces for a specific volume set for the data you have written to storage. If you had formatted all 20 members of WORM media for this volume set, you would now have 14 members that are no longer needed in the volume set they were created in.
Or you may find that one volume set requires more storage space than you initially calculated. Approaching your volume set creation process in this way allows you greater flexibility as your storage system grows and changes.
Note: Some exceptions to this would be if you needed to create a Fixed volume set or you were creating a volume set Target for use in a pair within the InveStore Backup program.
In conclusion, we recommend that you keep your volume sets logically organized and manageable in size and number, allowing InveStore to grow the volume-set as new surfaces are needed, better matching your actual storage needs.
Remember to keep in mind that careful planning and implementation of your volume sets at creation time will provide you with greater flexibility and manageability, as your storage system needs grow and change.