The InfiniSpares feature allows the InfiniBox system to keep working even when a preconfigured number of disks were failed. InfiniBox handles the increased number of failed drives by using unallocated capacity as spare capacity. Replacing the failed drives increases back the unallocated Capacity.
InfiniSpares improves the system ability to sustain mass disk failures at the expense of usable capacity.
Initially, the system allocates disks capacity according to the following:
- Reserved spares - up to 5% of the total capacity (this number varies across models, see below)
- The rest is divided between allocated and unallocated capacity, according to the actual usage
User data is written to the system
As new IO arrive at the system, the user capacity grows on the expense of the unallocated capacity. The amount of Reserved Spares is not affected.
In the example below (these numbers are only an example that illustrates the mechanism):
- User capacity - 40% of the total capacity
- Unallocated capacity - 57.5% of the total capacity (in this example, on F6000)
- Reserved Spares: 2.5% of the total capacity
Upon a disk failure
When a disk fails, the system uses some of the Reserved Spares for the rebuild process. When the failed disk is replaced, this capacity returns to the Reserved Spares.
As more and more disks fail
If the number of failed disks exceeds the number of Reserved Spares, some of the Unallocated Capacity is used for rebuild process. When the failed disks are replaced, this space returns to the Unallocated Capacity and then to the Reserved Spares.
As the unallocated capacity depletes
When the system Unallocated Capacity is exhausted, the system performs the following steps, regardless of the capacity distribution of User Capacity and Reserved Spares:
- The system no longer accepts writes.
- Upon the next drive failure, the system performs an emergency shutdown