Chapter 2. System overview 27
An example of chain weight 4.5 with one 24F, one 12F, and one 92F enclosures, all correctly 
cabled, is shown in Figure 2-10.
Figure 2-10   Connecting SAS cables while complying with maximum chain weight
2.5.10  RAID
When planning your network, consideration must be given to the type of RAID configuration. 
The Storwize V7000 supports either the traditional array configuration or the distributed array.
The IBM Storwize V7000 setup contains several internal disk drives, but these disk drives 
cannot be directly added to the storage pools. Disk drives must be included in a RAID to 
provide protection against the failure of individual drives.
These disk drives are referred to as members of the array. Each array has a RAID level. RAID 
levels provide various degrees of redundancy and performance, and have various restrictions 
regarding the number of members in the array. 
Apart from traditional disk arrays, IBM Spectrum Virtualize V7.6 introduced distributed RAID. 
Distributed RAID improves recovery time of failed disk drives in an array by distributing spare 
capacity between primary disks, rather than dedicating a whole spare drive for replacement.
IBM Storwize V7000 supports hot spare drives. When an array member drive fails, the system 
automatically replaces the failed member with a hot spare drive and rebuilds the array to 
restore its redundancy. Candidate and spare drives can be manually exchanged with array 
members.
Each array has a set of goals that describe the location and performance of each array. A 
sequence of drive failures and hot spare takeovers can leave an array unbalanced, with 
members that do not match these goals. The system automatically rebalances such arrays 
when the appropriate drives are available.