expanders (Enclosure Services Manager-ESM). Each ESM has an independent SCSI Enclosure Services (SES ) diagnostic processor.
The SAS disk drives or SSDs contained in the EXP12S are controlled by one or two PCIe or PCI-X SAS adapters connected to the EXP12S via SAS cables. The SAS cable will vary, depending upon the adapter being used, the operating system being used, and the protection desired.
•The large cache PCI-X (#5904/#5908) uses a SAS Y cable when a single port is running the EXP12S. A SAS X cable is used when a pair of adapters are used for controller redundancy.
•The medium cache PCI-X feature 5902 and PCIe feature 5903 adapters are always paired and use a SAS X cable to attach the feature 5886 I/O drawer.
•The zero cache PCI-X feature 5912 and PCIe feature 5901 use a SAS Y cable when a single port is running the EXP12S. A SAS X cable is used for AIX/Linux environments when a pair of adapters is used for controller redundancy.
In all of the above configurations, all 12 SAS bays are controlled by a single controller or a single pair of controllers.
A second EXP12S drawer can be attached to another drawer using two SAS EE cables, providing 24 SAS bays instead of 12 bays for the same SAS controller port. This is called cascading . In this configuration all 24 SAS bays are controlled by a single controller or a single pair of controllers.
Feature 5886 can also be directly attached to the SAS port on the rear of the Power 755, providing a very low-cost disk storage solution. When used this way, the imbedded SAS controllers augmented by the 175 MB write cache RAID enabler (#5679) in the system unit drive the disk drives in EXP12S. A second unit cannot be cascaded to a feature 5886 attached in this way.
Reliability, availability, and serviceability (RAS) features
Reliability, fault tolerance, and data correction
The reliability of systems starts with components, devices, and subsystems that are designed to be fault-tolerant. POWER7 uses lower voltage technology, improving reliability with stacked latches to reduce soft error (SER) susceptibility. During the design and development process, subsystems go through rigorous verification and integration testing processes. During system manufacturing, systems go through a thorough testing process to help ensure the highest level of product quality.
The system cache and memory offer ECC (error checking and correcting) fault- tolerant features. ECC is designed to correct environmentally induced, single-bit, intermittent memory failures and single-bit hard failures. With ECC, the likelihood of memory failures will be substantially reduced. ECC also provides double-bit memory error detection that helps protect data in the event of a double-bit memory failure.
The AIX operating system provides disk drive mirroring and disk drive controller duplexing. The Linux operating system supports disk drive mirroring (RAID 1) through software, while other RAID protection schemes are provided via hardware RAID adapters.
The Journaled File System, also known as JFS or JFS2, helps maintain file system consistency and reduces the likelihood of data loss when the system is abnormally halted due to a power failure. JFS, the recommended file system for 32-bit kernels, now supports extents on the Linux operating system. This feature is designed
to substantially reduce or eliminate fragmentation. Its successor, JFS2, is the recommended file system for 64-bit kernels.
With 64-bit addressing, a maximum file system size of 32 TB, and maximum file size of 16 TB, JFS2 is highly recommended for systems running the AIX operating system.
