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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.

Tipping Over of Cases

By far the most common damage to drives occurs through mechanical interference. The level of stress depends on the operational state of the drive, that is a drive that is not powered up will withstand some 300 G over 2 msec whereas in a drive that is up and running, 30 G suffice to cause errors and bad sectors. 30 G sounds rather high but any case tipping over and falling on a non-carpeted floor will easily exceed this value. The typical consequence is that the next bootup will terminate with the well known Chrrr, chrrr, chrrr ..... where the splash screen used to be.

Vibrations, Mortal Enemies of HDDs

Less dramatic but likewise common is the drumming on a somewhat fragile desk or bouncing of objects like bouncing balls of computer cases or simply hitting the case with the vacuum cleaner. This kind of scenario can cause vibrations that are the worst possible scenario for any HDD. If a drive can sustain a shock of 30-50G, the tolerance towards vibrations is usually only 1% of the shock tolerance. Typical values are in the order of 0.5-0.7G. It is happening every day. Transporting systems back and forth to LAN parties falls into the same category, in cases like that I always remove the HDD and transport it separately.

Power Outages In The Midst Of Defragmentation

A relatively rare cause of HDD failure is a power outage in the middle of a defragmentation but I have seen it happen and even though the damage is non-permanent in most cases, it may require a low level format which results in complete loss of all data.

HDTach and Similar Benchmark Programs

As nice as these programs are, repetitive use of HDTach and similar utilities add excessive stress to the drive. Even though failure may not occur immediately after benchmarking the drive they can weaken the drive and all it will take is another straw to break the camel's back. All those are factors that should be taken into account when yet another drive gets corrupted or dies. Sometimes it is just not the drive but a user pattern.

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