Dell EqualLogic PS6210XS EqualLogic Group Manager Administrator s Guide PS Ser - Page 128

You can also see these statistics through several CLI commands. Refer to the Dell EqualLogic Group Manager CLI Reference Guide for more information. Using Space-Borrowing Information Using information displayed in the GUI, you can see how space borrowing is affecting your system and answer the following questions: 1. Have I set my reserves too high or too low? 2. Am I benefiting from the borrowing feature? 3. Are any objects at risk of being deleted because they are borrowing space? 4. How much space can I use without causing objects within borrowed space to be deleted? The information on the Borrowed Space screen can help answer these questions. See the following table. Question Reserves too high or too low? Answer To determine if you have set the reserves too high or too low, you can see whether or not any object is borrowing and also the extent of the borrowing. For each volume or replica set, you can see the amount of space reserved and the amount of space in use. The amount of in-use space includes the amount of space that the snapshot or replica is borrowing. To determine whether the reserves are set appropriately, you should continually monitor the volume's snapshot or replica borrowing. Any benefits from borrowing? For objects that are borrowing space, you can monitor the number of snapshots or replicas to determine whether the correct number of them are being retained. Various GUI displays and CLI commands enable you to see this information. The GUI displays indicate on a per-pool basis whether borrowing is occurring and the extent of the borrowing. Additionally, you can see if a particular object is borrowing and whether replica sets on a partner are borrowing. Any objects at risk of being deleted? Any objects at risk of being deleted as the result of using too much space? You can determine if any objects are at risk of being deleted by monitoring whether an object is borrowing space. If no borrowing is occurring, the object is not at risk. To determine whether an object is at risk of being deleted, you can compare the amount of a resource that is being borrowed (such as snapshot reserve, replication reserve, or free pool space) to the amount that is not being used. About Compression of Snapshots and Replicas The compression feature maximizes available space within the storage pool by automatically targeting inactive snapshots and replicas and compressing them to reduce their storage footprint. When compression is enabled, the array periodically monitors activity to determine which snapshots and replicas can be safely compressed. Compressed data is automatically "rehydrated" (that is, decompressed) when that information needs to be accessed by the array. Compression is disabled by default on Dell EqualLogic arrays. If compression is enabled, it must remain enabled to provide access to already compressed data. Compression can be manually suspended and resumed, as needed, to prevent the array from compressing new snapshots and replicas, but any previously compressed data remains in its compressed state. When a compression-enabled member is part of a group containing other (non-compression) members, compressed data might be off-loaded to those other members, but this occurs only if the compression-enabled member becomes full of compressed data. When data is moved from one array to another, such as during a "vacate" action, the compressed data must be rehydrated first. After the data is moved, it is again eligible for compression if the new destination supports it. Compression can be enabled on any PS6210 or PS6610 array that is running compatible firmware. 128 PS Series Group Operations