This document describes the following failures: Disk failure This type of failure is the most commonly seen failure on your system. How often this failure occurs  depends on the use of the database. It is normal to see failures each month or even each week on larger  systems that are heavily used. Failure and replacement are done while the database remains online. After a disk failure, a regeneration process is started that copies data from the remaining dataslice copy to  a spare disk. Performance is decreased to 40% of original value until the regeneration process completes. The regeneration process is not the only process that slows down the system as it takes only 10% of  overall performance. The other 50% of performance degradation is the result of the difference in the  number of disks that are available before and after a failure. Before the failure, two disks deliver data for  each dataslice. After a failure, a single disk delivers data for two dataslices, which causes the 50%  performance degradation. It is this issue of one disk being available that is the drawback of parallel systems. Overall performance is  only as fast as the slowest component. The time a regeneration process runs depends on the amount of data it must copy. The copy time is 60 megabytes per second (MBps) on an idle system and 10 MBps on a system under  use. For example, if dataslices hold on average 100 GB of data, it takes approximately 10.000 seconds to  copy one dataslice on a system that is used (regeneration speed of 10 MBps). Because two dataslices  are on each disk, both dataslices must be copied. The total time that is needed to complete this copy is  approximately 20.000 seconds (6 hours). Disk failures are a concern only if spare disks are unavailable. Several components on a SPU can fail and regardless of which component fails, it is the SPU that fails.  (For this document, it does not matter which component causes the SPU failure.) The database is paused when a SPU fails, which interrupts any insert queries and select queries. The  pause lasts for approximately 20 minutes, but can be longer if the system does not detect any particular  error and attempts to power cycle the SPU to restore it to normal operation. Although there are situations in which a SPU fails and appears to be unresponsive, a power cycle often  clears the issue and there is no need for replacements. When the SPU fails, replacements can be made without any outage on the system. Because the SPU is  not used, it can be pulled from the system without affecting any other part of the system. Assessing Hardware Failures on IBM PureData System for Analytics N2001, N2002, and N3001 3 SPU failure SPU failures occur occasionally and are not seen often. Disk  SPU   ESM  Disk enclosure power supply  BlaceCenter power supply  BladeCenter blower  BladeCenter gig switch  Management switch  Host disk  Host  Rack power supply 