computer science

SCSI Enclosure Services

SCSI Enclosure Services is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand SCSI Enclosure Services rather than just read about it. In short: SCSI Enclosure Services (SES) is a protocol for more modern SCSI enclosure products. An initiator can communicate with the enclosure using a specialized set of SCSI commands to access power, cooling, and other non-data characteristics.

Key takeaways

SCSI Enclosure Services belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SCSI Enclosure Services to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SCSI Enclosure Services from memory before moving on to harder problems.

Reference excerpt

SCSI Enclosure Services (SES) is a protocol for more modern SCSI enclosure products. An initiator can communicate with the enclosure using a specialized set of SCSI commands to access power, cooling, and other non-data characteristics.

SES devices There are two major classes of SES devices:

Attached enclosure services devices allow SES communication through a logical unit within one SCSI disk drive located in the enclosure. The disk-drive then communicates with the enclosure by some other method, the only commonly used one being Enclosure Services Interface (ESI). In fault-tolerant enclosures, more than one disk-drive slot has ESI enabled to allow SES communications to continue even after the failure of any of the disk-drives. The definition of the ESI protocols is owned by an ANSI committee and defined in their specifications ANSI SFF-8067 and SFF-8045. Standalone enclosure services enclosures have a separate SES processor which occupies its own address on the SCSI bus. The protocol for this uses direct SCSI commands. An enclosure can be fault-tolerant by containing two SES processors.

SES commands The SCSI initiator communicates with an SES device using two SCSI commands: Send Diagnostic and Receive Diagnostic Results. Some universal SCSI commands such as Inquiry are also used with standalone enclosure services to perform basic functions such as initial discovery of the devices.

SES elements The SCSI Send Diagnostic and Receive Diagnostic Results commands can be addressed to a specific SES element in the enclosure. There are many different element codes defined to cover a wide range of devices. The most common SES elements are power supply, cooling fan, temperature sensor, and UPS. The SCSI command protocols assume that there may be more than one of each device type so they must be each given an 8-bit address. When an SES controller is interrogated for the status of an SES element, the response includes a 4-bit element status code. The most common element status codes are: 1h=OK, 2h=critical, 3h=warning, 5h=not installed.

SES element thresholds Some SES elements, such as voltage sensors, current sensors, and temperature sensors, have a thresholding function. This allows an enclosure to detect and report unacceptable environmental conditions. The SCSI standard allows for two different threshold levels, noncritical (warning) and critical. Also, each threshold has a minimum and maximum value. So for example the threshold values for the 12 volt power-supply could be set as follows:

Minimum critical - 10.8 volts Minimum noncritical - 11.4 volts Maximum noncritical - 12.6 volts Maximum critical - 13.2 volts Threshold values are set by a Send Diagnostic command to the Threshold Out diagnostic page (05h). Threshold values can be interrogated by a Receive Diagnostic Results command to the Threshold In diagnostic page (05h) with the PCV bit set to one.

Subenclosures A larger SCSI storage enclosure may contain multiple subenclosures. The subenclosure with address 00h is designated the primary subenclosure and can return information about the other subenclosures.

SCSI attached enclosure services SCSI attached enclosure services is a computer protocol used mainly with disk storage enclosures. It allows a host computer to communicate with the enclosure to access its power, cooling, and other non-data characteristics. The host computer communicates with the disks in the enclosure via a SCSI interface which may be Parallel SCSI, FC-AL, SAS, or SSA. One of the disk devices located in the enclosure is set up to allow SCSI Enclosure Services (SES) communication through a logical unit. The disk-drive then communicates with the SES processor in the enclosure, usually via Enclosure Services Interface (ESI), or a protocol called DSI for SSA enclosures. The data sent over the ESI or DSI interface is simply the contents of a SCSI command and the response to that command.

Implemented commands Only two SCSI commands are implemented by attached enclosure services devices:

SCSI standalone enclosure services SCSI standalone enclosure services is a computer protocol used mainly with disk storage enclosures. It allows a host computer to communicate with the enclosure to access its power, cooling, and other non-data characteristics. The host computer communicates with one or more SCSI Enclosure Services (SES) controllers in the enclosure via a SCSI interface which may be Parallel SCSI, FC-AL, SAS, or SSA. Each SES controller has a SCSI identity (address) and so can accept direct SCSI commands.

Implemented commands The following SCSI commands are implemented by standalone enclosure services devices:

Note 1: The initiator needs to send a SCSI inquiry to interrogate the SCCS bit which says whether the SES controller has this command.

See also SES-2 Enclosure Management SAF-TE — SCSI Attached Fault-Tolerant Enclosure SGPIO - Serial General Purpose Input/Output bioctl § SES hw.sensors

References

Worked examples

Example 1 — a first encounter with SCSI Enclosure Services

Start with the simplest possible case. Write down what SCSI Enclosure Services claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to SCSI Enclosure Services before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about SCSI Enclosure Services ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of SCSI Enclosure Services

In research: SCSI Enclosure Services appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses SCSI Enclosure Services in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: SCSI Enclosure Services is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer data storage, Computer hardware standards, Computer hardware tuning, so understanding it makes those chapters shorter.
In everyday life: Look for SCSI Enclosure Services outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study SCSI Enclosure Services in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SCSI Enclosure Services means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain SCSI Enclosure Services out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SCSI Enclosure Services in simple terms?

Why does SCSI Enclosure Services matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study SCSI Enclosure Services?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on SCSI Enclosure Services.