XS Server Hardware

This is a description of the first implementation of the School server. It describes the hardware and software implementation details, including the management of services. The actual services provided by the School server are described in the Server Services document, with an accompanying discussion of desired services.

Hardware Specifications

The School server hardware platform has not been selected at this time.

The current plan is to provide two hardware platforms. One, XSX, available by mid-March, will allow for School server software testing and early deployments in areas where power mains are at least periodic if not continuous. The second platform, XS, would be reduced in cost and power, and should be available for deployment beginning in October.

XSX Specifications

This is a version with a target date of mid-March. The primary goal is to support development of the School server/laptop software, including early trials.

The initial spec is similar to an OLPC laptop with attached USB hard drive and USB CD reader. The only defined aspect is an x86 family processor.

As this is a very limited production model (10s - 100 ?), flexibility wins out over cost. Consumer PC hardware is a possibility.

There are no power consumption targets for this device. A UPS may be suggested for trial deployments in areas of uncertain power.

XS Specifications

This is the hardware platform for actual deployment.

The school server must meet all of the environmental constraints of the XO laptop with the exception of daily rough handling!

Processor Architecture

This hardware platform may or may not be based on an x86 platform. Perhaps multiple hardware platforms will be supported.

Reasons to use x86

• Support required for only a single toolchain
• Able to use an XO as an emergency school server replacement ?

Reasons to use non-x86

• Lower power
• Lower cost
• Usually integrated with more onchip peripherals.

Network Interfaces

What network interfaces should be provided on the School server ?

802.11b/g

How many WiFi interfaces should be built into the server ? The current proposal is to include two distinct MACs.

If we really have 100 students in close proximity, can we make do with only two channels ?

The number of WiFi interfaces will be expanded using external USB connected WiFi nodes. A reasonable number of these (two to four) can be added to a server to increase the WiFi performance.

100baseT

A wired ethernet interface provides for reliable, high-bandwidth connection between school servers, or a school server and a DSL/satellite modem.

The current plan is to provide at least two 100baseT ports on the server (unless Powerline is substituted for one port).

Powerline

This technology has the potential to provide 100baseT performance over the power lines used to power the school server.

The advantage is that even if power lines aren't currently deployed in the school, the cable required for powerline networking is more likely to be available/cheaper than Cat-3 or Cat-5 cable.

A drawback is the lack of standardization and regulatory concerns in many nations. Correcting the regulatory situation isn't necessarily just a matter of time. Powerline networking emits strongly in the lower HF band, increasing the noise floor for existing communication systems (not WiFi, WiMax or cellular).

Other Interfaces

What other interfaces should the School server have ?

USB 2.0

A number of [Universal Serial Bus] (USB) 2.0 interfaces will be provided for extending the storage and communication capabilities of a School server.

Perhaps four ports, on two separate buses ? This assumes that up to two external ports will regularly be used to add additional WiFi channels (or the WAN connection), and two others will be available for external disk drives.

If no internal WiFi modules are included in the School server, then the number of USB ports should be increased by two.

Non-Volatile Storage

Internal Disk Drive

An internal disk drive will be provided. This may be either PATA or SATA. The size of this disk drive WILL vary, but a minimum size of 300 GB seems reasonable given a target of 100 students per server.

If the humidity environmental constraints require excessive encapsulation of internal drives, perhaps a single modular and "stackable" approach is optimum.

Otherwise, including the "first" drive internally reduces cost (less plastic enclosure).

External Disk Drives

Additional disks may be added using external USB 2.0 ports.

Flash

Enough flash (solid state non-volatile) memory should be provided on the server to allow the operating system and minimal services to continue operation even though the primary disk drive has failed. Current estimates are that 256 MB of memory will be sufficient for this task.

Power

The power specifications of the School server are important. Many schools do not have adequate, or regular, power. While the power consumption should be minimized (8W is a good target), consideration should be given to an integral (or optional modular) uninterruptible power supply (UPS). This is nothing more than a larger version of the laptop power supply!

In some test schools with minimal power, we are already deploying multiple (gang) battery chargers with integral UPS.

Possible methods of obtaining power are summarized in Battery_and_power.

Environmental

The environmental constraints on the School server are similar but slightly less constrained than those of the laptop, at least in terms of water and dirt penetration and drop resistance.

Temperature

The School server should meet the same environmental specifications for temperature as the laptop. This is 50 C ambient.

Water and Dust

This is one area where the School server doesn't have to meet the standards of the laptop. The server should be resistant to water exposure from a single direction (above), but does not have to survive immersion. It should be capable of operation in a constantly humid (100%) environment.

Can any hard drive operate at 100% humidity ? If the storage device needs to be encapsulated to meet humidity specs., it might as well be designed as separate, easy to replace modules (USB disk units.)

Dust intrusion should be considered. While the server will not contain a fan, it will be air cooled and dust collection on the cooling surfaces will be a problem. User cleanable filtration should be provided on the air intakes and vents.

Drop and Shake

The School server should meet the drop and shake specifications of standard consumer desktop PCs.

Perhaps the shake specification should be higher to account for rougher transport during deployment ?

Mounting

While the school server should be designed to sit on a flat surface, it should probably also be mountable (hangable) from a wall or post.

This shouldn't cause a problem unless the server includes batteries for a built-in UPS...

Software Specifications

The School server should run roughly the same Linux OS as that in the XO laptop. The release process will probably be different, but the kernel and most libraries should be identical.

Development Toolchain

What is the cost of this toolchain being different from that used for the XO laptop?

Upgrades

How is the School server upgraded ?

Service Management

How are services on the School server installed, configured, managed, and updated ?

A web based interface is a natural candidate for performing these actions on the School server.

Scalability

A School server should serve up to a hundred students. In schools with more students, how are the servers interconnected to minimize the management overhead ?

Ideally, the number of students supported by a single server results in at least two servers in a typical school, providing a degree of redundancy.

The management interface for a school should be independent of the number of servers needed to serve the school.