Blog posts for May 2011

First Canon

This is the first of seven Canons for Professional Engineers.  Applied more broadly, anyone engaged in the design and building of systems used by the public would do well to follow these pillars of responsibility.

These Canons are from a recent textbook for professional engineers published by McGraw Hill in 2010.  They are reproduced here for educational purposes (fair use).

Davis, Mackenzie L.
Design Principles and Practice
McGraw Hill: New York, 2010

First Canon

This canon is paramount. It is held superior to all the others.

Regulations, codes, and standards serve as the engineer’s guidance in ensuring that the facilities are safe and protect the health of the community. 

A large portion of this book and, for that matter, the education of environmental engineers is focused on these two issues. 

The public “welfare” is not articulated in regulations, codes, and standards. It is comprised of two parts: prosperity and happiness. 

The public prospers when the decisions of the professional result in economical projects. 

The public is “happy” when their trust and reliance on the professional is justified by successful completion of a project.

Economical projects do not imply the cheapest project. Rather, they imply projects that serve the client’s needs and satisfy the client’s elective options while conforming to regulatory constraints. 

In the classical engineering approach economical projects are achieved by the following:

  • Scoping of the engineering contract (Bockrath, 1986 and Sternbach, 1988).
  • Economic analysis of alternatives (GLUMRB, 2003; WEF, 1991; WPCF, 1977).
  • Selection of lowest responsible bidder (Bockrath, 1986) .
  • Diligent inspection of the work in progress (Firmage, 1980) .

In alternative approaches such as design-build, economy is achieved by alternate delivery methods.

At the beginning of a project, on approval of the selection of a specific consulting engineer, it is customary to hold a “scope meeting.”

At the scope meeting a typical agenda includes (Firmage,
1980 and Sternbach, 1988):

  • Identification of primary contacts for the owner and engineering firm.
  • Scope and extent of engineering work.
  • Starting and completion dates.
  • Construction inspection.
  • Responsibility for allied engineering services.
  • Procedures for out-of-scope requests.
  • The fee.

Many times these items are addressed in the engineering firm’s proposal.  In the proposal process, the clarity with which these are addressed may serve as a basis for selection of the engineering firm.

The scope and extent of engineering work should be explicitly defined, in writing, to avoid misunderstanding. 

The scope ensures that the client understands the limits of the work the engineer is willing and/or able to perform.

It provides the engineer with a framework for establishing the fee and level of effort to be provided as well as ensuring that the engineer is not expected to perform work outside of the area of competence.  

It may include such things as personnel assigned to the project, their qualifications and responsibilities, evaluation of alternatives, design of the facility, preparing detail drawings, cost estimates, evaluating bids, as well as bidder qualifications, surveying, staking the project, preparation of operation and maintenance manuals, attendance at meetings, and documentation.

The starting and completion dates provide both the client and the engineer with realistic expectations as to the progress of the project.

The scope meeting should identify the design engineer’s responsibilities for construction inspection. 

Typically, the design engineering firm provides a field engineer and/or a construction observer to diligently observe and, to the best of their ability, assure the owner that the construction is taking place in accordance with the plans and specifications as the project is being built.

Although a field engineer from a firm not involved in the design may be retained, it is preferable that the design firm provide the engineer to ensure continuity. 

While construction observers may be competent to do routine examinations of the progress of work, they generally do not have the technical background to assure compliance with design specifications unless they are given specific training. 

For large projects, a full-time field engineer is on site. For small projects, periodic inspection and inspection at critical construction milestones is provided.

Small engineering firms may not have the expertise to provide the design specifications for all of the components of the design. In this instance, the responsibility for providing allied engineering services such as geotechnical/soils consultants and electrical, mechanical, and structural engineering as well as architectural services should be spelled out in writing at the scope meeting.

The professional engineering qualifications of those supplying the allied engineering should also be explicitly defined. 

For example, structural engineers that specialize in building design may not
be appropriate for designing structures subject to aggressive wastewater.

Billing schedules and expectations of payment are also included in the scope meeting.  Economic analysis of alternatives, selection of lowest responsible bidder, and diligent inspection of the work in progress will be relevant to the design discussion that follows.

Second Canon

Professional Engineer's Second Canon

Engineers are smart, confident people. With experience, we gain wisdom. The flaw of our nature is to overextend our wisdom to areas not included in our experience.

Great care must be taken to limit engineering services to areas of competence. Jobs may be too large, too complicated, require technology or techniques that are not within our experience. 

Competence gained by education or by supervised on-the-job training sets the boundaries on the areas in which we can provide service. Others more qualified must be called upon to provide service beyond these experiences.

Engineers are creative. We pride ourselves in developing innovative solutions. We believe that civilization advances with advances in technology. Someone has to build the first pyramid, the first iron bridge, the first sand filter. Many times “the first” design fails (Petroski, 1985).

Thus, there may be a conflict between creativity and service in an area of competence. The conflict must be resolved very carefully. Although safety factors, bench and pilot scale experiments, and computer simulations may be used, the client and professional must, in a very explicit way, agree on a venture into uncharted territory. 

If the territory is simply uncharted for the design engineer but not for the profession, then the design engineer must employ a partner that can bring
experience or obtain the necessary training to become competent.

Third Canon

It may not seem that engineers would be called upon to issue public statements. Yet, there are numerous times that public statements are issued. 

Often these are formal, such as signing contracts, making presentations to a city council or other public body, and issuing statements to the news media. 

In other instances it is not so obvious that the statements are public. Verbal statements to individual members of the public, posting of signs, and signing change orders on government financed projects are examples of informal public statements.

Fourth Canon

A faithful agent is more than a loyal one. A faithful agent must be completely frank and open with his/her employer and client. This means getting the facts, explaining them, and not violating the other canons to please the client or your employer.

Conflicts of interest may be subtle. A free lunch, a free trip, or a golf outing may not seem like much of a conflict of interest, but in the eyes of the public, any gift may be seen as an attempt to gain favors. Appearances do count and, in the public’s view, perception is reality.

Fifth Canon

This canon appears to be self-explanatory. We understand that cheating on exams is unethical.  Likewise, cheating by claiming credit for work that someone else has done is unethical.

Unfair competition has taken a broad meaning in the review of ethics boards.  For example, offering services to a potential client that has retained another engineer to do the same work falls into the category of unfair competition if the engineer solicits the work.

The circumstances are different if the client solicits the engineer after having already retained another engineer. This type of request must be treated with great care.  It is best to decline this type of employment until the client and original engineer resolve or dissolve their relationship.

Similarly, a request to review the work of another engineering firm may be construed to be unfair competition.  The best procedure is for the client to advise the original firm of their desire to have an independent review. 

Another alternative is to advise the originating engineering firm
that the request has been made. This is a matter of courtesy, if not a matter of ethics.

Sixth Canon

This canon has two elements. 

  • The first is to treat others with the same courtesy that you would expect from them. 
  • The second is to behave such that the credibility of your work is not jeopardized.

Seventh Canon

Engineers use technology both in the process of doing their job and in the provision of solutions to problems. 

It is incumbent on them to keep up with the technology. 

One of the best means of doing this is to participate in one of the relevant professional societies by attending meetings, reading journal articles, and participating in workshops.

SSD choices

NAND flash reliability

At the time of this writing, all SSD are NAND flash-based designs.  NAND flash, like EEPROM, was designed with "pages" of memory that must be "flashed" back to binary 1's prior to a write cycle that would set/change any of the contents on a given page.  Page sizes vary but are usually 2**x where x > 8.

Floating gate NAND designs are the most reliable but wear out (become less reliable) with about a million erase cycles.  Plain SLC (single-level cell) NAND gates wear out on the order of 100,000 erase cycles.  Plain MLC (multilevel cell) NAND gates wear out on the order of 10,000 erase cycles.

Commercial-grade SSD

If memory serves, Sun's Fishworks group researched several STEC SSD products when building their "logzilla" project to speed up ZFS.  The STEC ZeusIOPS product family is the current offering.  They support FC/AL, SAS and SATA interfaces in 2.5" and 3.5" form factors.   I'd like to evaluate for my filesystem journals.  STEC products incorporate ECC and TRIM support.  I would guess 3.5" SAS may turn out to be the preferred form factor going forward.

I'd put Pliant's Lightning product on my 2.5" SAS form factor short list.  Lightning includes ECC and TRIM.

Home-use SSD

For non-mission critical 3.5" SATA-II use, the OCZ Vertex 2 EX line lacks ECC but should be affordable since it is a MLC-based design.  Vertex 3 (SATA-III interface) is now available also.  Both Vertex 2 and 3 support TRIM.

And then there are the (non-persistent) DRAM-based solutions.  I can't recommend using these for anything other than temporary data.  These aren't appropriate for a filesystem journal.


To give the SSD micro-controller a hint about which pages can be preemptively flashed before needed for writing, the Operating System must send TRIM commands to the SSD whenever a filesystem page becomes deallocated or otherwise unreferenced.


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