TRAS Violation: The Creeping Corruption of a HDD
One of the most common reasons for HDD failure is what is called tRAS violation. tRAS is the minimum bank open time of the DRAM, that is, we are talking about system memory here. Many mainboard manufacturer still include Ultra and Turbo settings in their CMOS setup options that are only workable at 100 MHz memory bus settings, a.k.a PC1600 mode. One setting that has absolutely no impact on performance is the minimum bank open time or tRAS, while the same setting can have catastrophic consequences for data integrity including HDD addressing schemes if the latency is set too short. In theory, tRAS can be as short as tRCD + CAS delay, however, in reality, the minimum bank open time is dictated by the RAS Pulse Width, that is the time required to reach a voltage differential between memory bitlines and reference lines to safely identify a 0 or 1 logical state.
The main reason why tRAS violation does commonly lead to HDD corruption may relate to the translation of the physical memory space into virtual memory sub-spaces by the operating system and finally writing the data back to the storage media but it is not entirely clear what is going on there. A fact is, though, that a tRAS value of 5 is adequate for PC1600 or 100 MHz operation. At 133 Mz or PC2100, tRAS should never undercut 6T, likewise, at PC2700, the value should be increased to 7T where applicable. In terms of performance, tRAS settings hardly make any difference. We challenged some performance gurus at AMD on this matter and they reported a drop in Quake frame rates from 792 fps to 790 fps when increasing tRAS from 5T to 6T.