content_image/1001432.jpg
Depending on the selected RAID level and sparing requirements, six types of arrays are possible, as shown in Figure 4-3. 

<img src='content_image/1001432.jpg'>

Tip:  Remember that larger drives have a longer rebuild time. Only RAID 6 can recover from a second error during a rebuild due to the extra parity. RAID 6 is the best choice for systems that require high availability, and is therefore the default. 

## 4.3.3 Ranks 

After the arrays are created, the next task is to define a rank . A rank is a logical representation of the physical array formatted for use as FB or CKD storage types. In the DS8880, ranks are defined in a one-to-one relationship to arrays. Before you define any ranks, you must decide whether you will encrypt the data. 

## Encryption group 

All drives that are offered in the DS8880 are Full Disk Encryption (FDE)-capable to secure critical data. In the DS8880, the Encryption Authorization license is included in the Base Function license group. 

If you plan to use encryption, you must define an encryption group  before any ranks are created . The DS8880 supports only one encryption group. All ranks must be in this encryption group. The encryption group is an attribute of a rank. Therefore, your choice is to encrypt everything or nothing. If you want to enable encryption later (create an encryption group), all ranks must be deleted and re-created, which means that your data is also deleted. 

For more information, see the latest version of IBM DS8880 Data-at-rest Encryption , REDP-4500. 

