IBM has begun reshipping its low-end S/390 server, despite failing to pin down a fix for the problems that have blighted the system since its launch last September.
The server giant was forced to stop shipping its Multiprise 3000 system to users earlier this year after failing to produce a fix for a software glitch in its internal management software. This caused some models to crash.
So far, a third of all systems shipped have needed repair work, with more than one in seven suffering from "unexpected downtime". IBM has sold around 200 Multiprises since the launch.
The problem arises in the internal microcode that the S/390 platform uses to control and manage its internal systems.
In certain configurations, the machine closes down when its workload reaches a certain level.
IBM is said to be confident that it has identified the configurations and workloads that cause the crash, and that it is safe to ship to customers who will not use it in those situations.
IBM is recommending that customers who may be affected wait until the software fix is available. The company hopes that will be at the end of this month.
The problems have been highly embarrassing for IBM as it contradicts claims for the S/390's main strength, robustness.
Even worse, the company has been forced to concede that insufficient testing is to blame, undermining IBM's famed reputation for vigorous quality control.
"With software faults, you're looking at very long lead times for testing," said Phil Payne, an analyst at Isham Research. "Corporate customers need to be reassured that enough testing time has gone in if they are going to trust the product."
Multiprise is targeted at medium-sized firms or large corporate customers running a single legacy application.
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