Format Volume Set: Step 2
Step 2: There are several parameters by which you may format a given volume set:
· Write Order- The Write Order or MAP_SCHEME determines the order to which volume members are written. If CONTIGUOUS mapping is chosen, the flip side of a volume is used before progressing to the next volume. If STAGGERED mapping is used, the A-sides of all the volumes in a volume set are used, then the B-side.
· Volume Set Type- EXTENSIBILITY affects whether and how new volumes may be added to the volume set you are creating. Fixed extensibility means the number of volumes in the set is permanently fixed at format time. Manual extensibility means that only the user can add volumes to the volume set. Automatic extensibility means that the system can automatically add erased or re-useable surfaces to the volume set as needed. If the volume set is automatically extensible, it is also manually extensible.
Important Note: Automatic is the default extensibility setting. The Volume Set Type is permanently set at the time of creating the volume set, and cannot be changed at a later time.
· Format Type- At this time, this is limited to PEGASUS_ARCHIVE_FILESYSTEM.
· Directory and File Creation Watermark- To minimize disc thrashing, InveStore clusters related files and subdirectories on the same volume (as opposed to having the files scattered randomly over many volumes within a volume set). InveStore also avoids having files span volumes, since any access to such a file would very likely cause thrashing.
However, InveStore will not require clustering, since in some scenarios (backups or chronological archiving of data with no updates, for example) simply filling up the volumes sequentially is the best strategy. To facilitate these goals, we do the following:
1. A file is always written to the same volume that contains its parent sub-directory, if possible.
2. A sub-directory is always written to the same volume that contains its parent sub-directory, if possible.
3. Volume sets have a user-defined File Creation Watermark value. This value determines how full a volume can get before we quit writing new files to it. For example, if the File Creation Watermark value is 80%, and the volume is over 80% full, writing a new file to that volume set will cause its parent subdirectory to be extended to a new member volume and the new file written there. File modifications, on the other hand, will be written to the same volume as the original file even if the File Creation Watermark has been exceeded.
4. Volume sets have a user-defined Directory Creation Watermark value. This value determines how full a volume can get before we quit creating new directories on it. This leaves room to add files to existing directories without having to extend them.
5. InveStore also allows the user to specify which volume he wants a subdirectory (and its subsequent child subdirectories and files) to be created on or extended to. So, for example, if the user knows that some subdirectory is going to be frequently modified, while the others written once, they may wish to create that subdirectory on the last volume in the set so that its data will stay together.
In a case where the user was just copying data to storage, with, say XCOPY /s, they should set both watermarks to 100%, since the data is naturally clustered already. If files are frequently copied to old subdirectories, but never modified, the File Creation Watermark should be at 100% and the Subdirectory Creation Watermark at something like 50%. If files are frequently modified, the File Creation Watermark should be less than 100%.
The default Watermark values as well as existing Watermark values for a given volume set may be modified by the administrator.
Note: Though the watermark values are defined for each volume set, they are only enforced on individual member volumes—the extent to which a volume set is full has nothing to do with watermarks.
· Please Select the Media Group to Format- You MUST select and hi-light the media group to format from the listed groups. The groups listed are not interchangeable.
· Number of Surfaces- At the time of format you must determine the number of surfaces that you want allocate for use in the creation of the new volume set. This is based on the Volume Set Type (Fixed, Manual and Automatic extensible), and involves determining the Minimum and Maximum number of surfaces used.
Important Note: Single surface volume sets must be set to a Volume Set Type of Fixed. This allows one-surface, one sub-directory volume sets as created in InveStore v3.
The Minimum number of surfaces is the number of surfaces that will be used in the initial creation of the volume set at format time. In some cases you may desire to start with a smaller minimum initial size, keeping free the available pool of surfaces to all volume sets in the storage server.
When using MO media (which is double-sided media) the minimum number must be set to an even number starting with 2 unless the Volume Set Type is a Fixed volume set.
When using DVD-RAM media (which is single-sided media) the minimum number may be set to any number starting with 1.
Note: For Fixed sets, the minimum number will also be the maximum number.
This is the total number of surfaces that the new volume set may grow up to. When the Volume Set Type is set to either Manual or Automatic, the Maximum number of surfaces must exceed the minimum number of surfaces being formatted and be sufficient for the storage space needed for your data set.
When using MO media (which is double-sided media) the maximum number must be set to an even number.
When using DVD-RAM media (which is single-sided media) the maximum number may be set to any number, even or odd.
This is a format option that causes re-writable volume sets to be re-initialized after all the files & directories on the surfaces of the volume set have been deleted by an application.
Once you have set the parameters in Step 2 to the desired settings, select the Format button to start the process. A progress indicator will advise you on the status of the format process. Once the format has completed, you will see the new volume set and it’s members displayed under the Volume Sets view.