Independent channel recovery with replay buffers on all interfaces allows recovery of a single DIMM channel, while other channels remain active. Further redundancies are incorporated in I/O pins for clock lines to main memory, which eliminates the loss of memory clocks because of connector (pin) failure. The following RAS enhancements reduce service complexity: 

## 9.5 Reducing touches 

GLYPH<SM590000> Continued use of RAIM ECC. 

GLYPH<SM590000> No cascading of memory DIMM to simplify the recovery design. 

GLYPH<SM590000> Replay buffer for hardware retry on soft errors on the main memory interface. 

GLYPH<SM590000> Redundant I/O pins for clock lines to main memory. 

IBM Z RAS efforts focus on the reduction of unscheduled, scheduled, planned, and unplanned outages. IBM Z technology has a long history of demonstrated RAS improvements, and this effort continues with changes that reduce service touches  on the system. 

Firmware was updated to improve filtering and resolution of errors that do not require action. Enhanced integrated sparing in processor cores, cache relocates, N+1 SEEPROM and POL N+2 redundancies, and DRAM marking also are incorporated to reduce touches. The following RAS enhancements reduce service touches: 

GLYPH<SM590000> Improved error resolution to enable filtering 

GLYPH<SM590000> Enhanced integrated sparing in processor cores 

GLYPH<SM590000> Cache relocates 

GLYPH<SM590000> N+1 SEEPROM 

GLYPH<SM590000> N+2 POL 

GLYPH<SM590000> DRAM marking 

GLYPH<SM590000> (Dynamic) Spare lanes for PU-SC, PU-PU, PU-mem, and SC-SMP fabric 

GLYPH<SM590000> N+1 radiator pumps, controllers, blowers, and sensors 

GLYPH<SM590000> N+1 Ethernet switches 

GLYPH<SM590000> N+1 Support Element (SE) (with N+1 SE power supplies) 

GLYPH<SM590000> Redundant SEEPROM on memory DIMM 

GLYPH<SM590000> Redundant temperature sensor (one SEEPROM and one temperature sensor per I 2 C bus) 

## 9.6 z15 availability characteristics 

GLYPH<SM590000> FICON forward error correction 

The following functions include availability characteristics on z15 servers: 

GLYPH<SM590000> Enhanced drawer availability (EDA) 

EDA is a procedure  under which a CPC drawer in a multidrawer system can be removed and reinstalled during an upgrade or repair action with no effect on the workload. 

GLYPH<SM590000> Concurrent memory upgrade or replacement 

Memory can be upgraded concurrently by using Licensed Internal Code Configuration Control (LICCC) if physical memory is available on the drawers. 

