IBM DS8000 Disk scrubbing, Battery backup units, Rack cooling fans, Rack power control card RPC

4.6.6 Disk scrubbing

The DS8000 will periodically read all sectors on a disk. This is designed to occur without any interference with application performance. If ECC-correctable bad bits are identified, the bits are corrected immediately by the DS8000. This reduces the possibility of multiple bad bits accumulating in a sector beyond the ability of ECC to correct them. If a sector contains data that is beyond ECC's ability to correct, then RAID is used to regenerate the data and write a new copy onto a spare sector of the disk. This scrubbing process applies to both array members and spare DDMs.

4.7 Power and cooling

The DS8000 has completely redundant power and cooling. Every power supply and cooling fan in the DS8000 operates in what is known as N+1 mode. This means that there is always at least one more power supply, cooling fan, or battery than is required for normal operation. In most cases this simply means duplication.

Primary power supplies

Each frame has two primary power supplies (PPS). Each PPS produces voltages for two different areas of the machine:

￿208V is produced to be supplied to each I/O enclosure and each processor complex. This voltage is placed by each supply onto two redundant power buses.

￿12V and 5V is produced to be supplied to the disk enclosures.

If either PPS fails, the other can continue to supply all required voltage to all power buses in that frame. The PPS can be replaced concurrently.

Important: It should be noted that if you install the DS8000 such that both primary power supplies are attached to the same circuit breaker or the same switch board, then the DS8000 will not be well protected from external power failures. This is a very common cause of unplanned outages.

Battery backup units

Each frame with I/O enclosures, or every frame if the power line disturbance feature is installed, will have battery backup units (BBU). Each BBU can be replaced concurrently, provided no more than one BBU is unavailable at any one time. The DS8000 BBUs have a planned working life of at least four years.

Rack cooling fans

Each frame has a cooling fan plenum located above the disk enclosures. The fans in this plenum draw air from the front of the DDMs and then move it out through the top of the frame. There are multiple redundant fans in each enclosure. Each fan can be replaced concurrently.

Rack power control card (RPC)

The rack power control cards are part of the power management infrastructure of the DS8000. There are two RPC cards for redundancy. Each card can independently control power for the entire DS8000.

Chapter 4. RAS 79