Potentially Hard Disk Manufacturers, equipment suppliers and Data Center Managers tend to blame it on Electrostatic discharge (ESD), based on the fact that with increasing recording density and shrinking size of giant magnetoresistive (GMR) read/write heads, the GMR sensor is getting more sensitive to electrostatic discharge (ESD) events.
Some kinds of ESD damages will cause soft magnetic degradations of head performance with a progressive nature. We have reports of head degradations by ESD damages as well as other damages due to head scratches and electro-migration effects of GMR stack. It is usually very difficult to distinguish these phenomena explicitly by QST (quasistatic tester) and spinstand measurement test.
Most data center managers believing it to be caused by ESD, end up investing thousands of Dollars ($) in undertaking power quality audits for their facility, when actually the real culprit is “Contamination”. Did not expect this right? well yes it is.
What kind of Contamination causes Hard Disk / Mother Board failures?
Contamination, especially gaseous contamination, often results from the bacterial break down of sulfates in organic matter in the absence of oxygen, such as in swamps and sewers (anaerobic digestion). It also occurs in volcanic gases, natural gas and some well waters.
The predominant gas resulting from such places is Hydrogen sulphide and is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is partially responsible for the foul odor of rotten eggs and flatulence. The odor of H2S is commonly misattributed to elemental sulfur, which is in fact odorless. H2S has been predominantly found in areas running large sewers, Industrialised town ships with polluting industries, reclaimed land (built over swamps), etc.
I need not mention how many sewers run across some of our cities which are home to many data Centers, Noida, near New Delhi (India) being one of the predominant ones. Mumbai & Bangalore which house 80% of Data Centers in India are leading the pack with the highest levels of contamination.
ANSI/ISA-S71.04-1985
The American National Standard for Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants was designed to classify airborne contaminants that may affect process measurement and control instruments.
The classification system provides users and manufacturers of instruments / equipment with a means of specifying the type and concentration of airborne contaminants to which a specified instrument / equipment may be exposed.
Two methods have been used for environmental characterization. One is a direct measure of selected gaseous air pollutants. The other, which can be termed "reactivity monitoring," provides a quantitative measure of the overall corrosion potential of an environment.
Pollution analysis may provide short-term estimates for specific sites. High values will confirm that a severe environment exists. The reverse, however, is not necessarily true. Industrial environments may contain a complex mixture of contaminants that interact to greatly accelerate (or retard) the corrosive action of individual gas species.
To avoid these practical difficulties, the nature of industrial environments is defined in terms of the
rate at which they react with copper. As a direct measure of overall corrosion potential, reactivity
monitoring involves the placement of specially prepared copper coupons in the operating environments. Copper has been selected as the coupon material because data exists which correlates copper film formation with reactive (corrosive) environments. It has proven to be particularly useful for environmental characterization. Analyses may consist of measurements of film thickness, film chemistry, or weight loss. Sensitivity of reported techniques is well within the range required for meaningful application data. In addition to the use of a copper strip a silver strip is also used. Note that Silver (Ag) results are not officially part of the ISA/ANSI S71.04 standard. These results are used to confirm copper (Cu) results, to identify potential chloride contaminants, and they provide potential identification of the specific sulfides causing corrosion
Four levels of corrosion severity are established as shown below.
There is a broad distribution of contaminant concentrations and reactivity levels existing within industries using process measurement and control equipment. Some environments are severely corrosive, while others are mild. The purpose of the contaminant classes is to define environments on the basis of corrosion rate of oxygen-free high conductivity copper.
Severity level G1
Mild — An environment sufficiently well-controlled such that corrosion is not a factor in determining equipment reliability.
Severity level G2
Moderate — An environment in which the effects of corrosion are measurable and may be a factor in determining equipment reliability.
Severity level G3
Harsh — An environment in which there is a high probability that corrosive attack will occur. These harsh levels should prompt further evaluation resulting in environmental controls or specially designed and packaged equipment.
Severity level GX
Severe — An environment in which only specially designed and packaged equipment would be expected to survive. Specifications for equipment in this class are a matter of negotiation between user and supplier.
Solution
There are very few companies in Asia that are capable of providing such a service tailored especially for the data center environments. This is a professional service and has to be delivered very carefully for accurate results. Based on the contamination identified a proper mix of Media and a proper Air purification system designed for use in data centers needs to be selected.
There are a number of issues which must be addressed in the selection of an air purification system.
• The first issue is to identify the types and concentrations of contaminants that will need to be removed. This information will be available from the corrosion chemical analysis report made available from coupon testing.
• The second issue is to determine the minimum airflow requirements for dealing with the contaminants. On odor control applications source capture will usually provide significantly less airflow requirements than a general ventilation approach, but general ventilation will normally need to be used where personnel are operating within the contaminated space.
• The third issue is to confirm any physical limitations for the equipment, anticipating all regular maintenance and media change out requirements.
After selection of the Unit the next step will be:
1. Determine the type of chemistry or chemistries that are best able to remove the contaminant(s). There are usually several options for the removal of most vapour phase contaminants, but there is usually one approach that will be more efficient, or cost effective than others.
2. Next, decide whether a cell type (light duty system) or a deep bed (heavy duty system) is required for the application. This will depend on the nature and concentration of the contaminant and the tolerance and lifespan of the media bed for retention of these contaminants.
3. The next step is to confirm the materials of construction to suit the corrosive environment.
4. The next step is to determine whether blow through or draw through configurations are preferred. Blow through is usually used for corrosion control applications, and draw through is usually used for odor control applications.
5. The next step is to determine pre and after filter requirements. The prefiltering is necessary to prevent the chemical media from being blinded from upstream particulates or mists, and normally requires a 40% roughing filter followed by a 95% after filter. Coalescing and mist eliminators and grease filters are used where moist conditions exist upstream of the air purification equipment. Final filtering is used only where it is important to eliminate any of the fine dust that may come off the media when it is first started up after a media changeout. This usually requires a 95% filter to capture this fine particulate.
6. The next step is to confirm any auxiliary requirements, including preheat, precool or humidification requirements necessary for the application.
A good idea would be to select a system designed in compliance to the ASHRAE standards.
Specifications of Media to be used (Note: these are specifically for the case of H2S contamination)
General Description: Spherical or cylindrical porous pellets formed from a combination of powdered activated alumina and other binders, suitably impregnated with potassium permanganate to provide ptimum adsorption, absorption, and oxidation of a wide variety of gaseous contaminants.
Removal Capacity:
• Hydrogen Sulfide: 0.13 g/cc min (16 % by weight)
• Sulfur Dioxide: 0.06 g/cc min (3.5% by weight)
• Nitric Oxide: 0.06 g/cc min (2.5% by weight)
• Nitrogen Dioxide: 0.016 g/cc min (1.0 % by weight)
• Formaldehyde: 0.023 g/cc min (1.4% by weight)
Manufacturing Quality Assurance Standards:
• Leach test (indication of porosity)- 180 minute or less
• Permanganate content: 8 % minimum
• Moisture Content: 20 % maximum
• Crush Strength: 40 to 60 %
• Abrasion Loss: 3.0 % maximum
• Nominal pellet Diameter: 1/8” (approximately 4 mm), 85% after screening
This post is also available as a published white paper written by the author at http://bdstrategy.asia/data-center/power-and-cooling/214-hardware-failure-look-beyond-power-a-cooling
References: Wikipedia, ANSI/ISA-S71.04-1985 standard, ASHRAE standards.
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