Dell PowerVault DP500 - Manual (Page 8)

8
Expanding Disk Storage
The total storage space in use for these two servers is 350GB. The system
administrator must factor in an estimated storage space growth of 10 percent
over the next four years resulting in approximately 500GB of data that must
be protected.
The "Allocating Space for Protection Groups" section in Planning a System
Center Data Protection Manager 2007 Deployment describes the methodology
DPM uses to allocate space requirements for protection groups. Using
computations based on 500GB of protected data results in the following
estimates:
From the above example, five 250GB drives provide 1TB of usable storage
space. In a RAID 5 configuration, the space equivalent of one physical disk
stores parity data used to recover data in case of single disk failure.
Approximately 250GB of the total disk space is dedicated to parity. The
available space for DPM's data pool is four times 250GB, or 1TB total
(Figure 2-1).
NOTE:
The parity data is distributed across all of the physical disks. The total space
used for parity equals one physical disk.
Figure 2-1. Logical View of Disk Space Usage in a RAID 5 Group of N Physical Disks
Storage space for the initial (replica) backup 623GB
Storage space for recovery points 376GB
Total additional DPM space (estimated) 1TB
1 2 N - 1 N(Parity)