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In the event of a DDM failure, the ESS can regenerate data from the other DDMs in
the array.
Non-RAID disk group support
The ESS supports non-RAID arrays also. If you format the DDMs as a non-RAID
group, then the array is a single DDM.
Predictive failure analysis
The DDMs in the ESS provide state-of-the-art failure analysis techniques that
predict errors before they affect data availability.
The DDM, which is continuously performing predictive failure analysis of device
failure conditions, notifies the IBM Enterprise Storage Server of impending hardware
failures.
Failover protection
The ESS includes the failover protection feature.
If one of the clusters fails, the ESS temporarily transfers all ports over to the
remaining cluster so that data access can continue. See "Nonvolatile storage" on
page 16 for additional information on cluster redundancy.
Sparing
The sparing function of the ESS is automatically called whenever a DDM failure is
detected. The ESS maintains data access during the sparing operation.
Note: The first two arrays on a loop include a spare.
When the ESS detects a DDM failure in a loop, it automatically uses a spare DDM
to replace the failing DDM. The ESS reconstructs the data on the spare DDM by
using redundant information from the remaining DDMs in the array.
If a DDM fails, a loop reconfigures itself into two loops. Once service personnel
have replaced the DDM, the loop automatically resumes normal operation as a
single loop. Neither the host system nor the operator needs to take any action.
Fibre-channel support
The ESS provides fibre-channel connection when your IBM SSR installs a
Fibre-channel adapter card (short wave) in the ESS. See "Fibre-channel
connection" on page 10 for a description of fibre-channel topologies that are
supported by the ESS.
For more information on host adapters and operating system attachments that the
ESS supports on the fibre-channel adapter see the ESS Web site:
IBM also provides fibre-channel connection through the IBM 2108 SAN Data
Gateway, Model G07. You can get the details on fibre-capable server models,
adapters, and operating systems on the Web at:
1. Disk storage on an ESS is available in a package of eight DDMs, which IBM calls an 8-pack.
http://www.storage.ibm.com/hardsoft/products/ess/supserver.htm
http://www.ibm.com/storage/SANGateway
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Chapter 1. Introduction
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