XS Recommended Hardware
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This is a description of the hardware recommended for the School server. Unlike the current laptop, the school server is currently off-the-shelf (OTS) hardware. This document outlines general criteria for the School Server and has some specific notes about what we recommend for the XS.
Overview
Overall considerations
- Known to be compatible with Fedora (Fedora 7 / Fedora 9) which is a modern Linux distribution.
- Low power consumption
- Operation in environmentally challenging conditions
Hardware known to work
This hardware has been tested with the XS images - add your own, if possible with nots as to its suitability for the rule
- HP/Compaq dx2250 - used by Martin Langhoff as test XS, low memory. Is RH-certified, and ships with a factory RH install.
- Laptop Dell Latitude D380 - used by Martin Langhoff as test XS.
- Dell PowerEdge SC440 - used by Martin Langhoff as test XS.
As our work is based on a Fedora Linux, the Hardware compatibility notes for Fedora and RH systems is the best guide. See:
- RedHat's Certified Hardware list
- Notes on HCLs for Fedora and Smolt
- Fedora HCL - appears temporarily abandoned, but Smolt
- Smolt stats can be of use to see whether a particular HW is used in the field with Fedora systems - see the stats page - the page explains how it works.
Processor
Network Interfaces
The following are the integrated networking interfaces on XS. Additional interfaces may be added to the system using the peripheral interfaces.
Wireless Mesh
The School server will have two or three Active Antenna, an 802.11b/g WiFi wireless mesh networking interface. Each one of these serves as a mesh portal point operating on one of the three non-overlapping 802.11b channels (1, 6, and 11).
While connected to the school servers using detachable five meter USB cables, the Active Antennas are considered integrated as there must always be at least one of these connected for proper server operation. In the future, higher numbers (four or five) of more advanced (directional) Active Antennas may be used.
These are not integrated physically into the XS school server. This allows them to be located optimally for RF transmission/reception, while the server is in a more accessible location. It also allows for greater separation of the three antennas, operating simultaneously at neighboring frequencies.
Wired Networking
Providing at least two wired ethernet interfaces allows for reliable, high-bandwidth connection between a school server and its internet connection (if through a DSL or satellite modem), other school servers, and any non-laptop computer equipment.
The current plan for XS is to provide two 1000baseT ports and four 100baseT ports on the server. The two high speed ports allow multiple servers in a school to form a high speed backbone, and the four additional ports on each server provide school network expansion without using external switches. External switches are not encouraged, due to unknown quality and the requirement of external power.
Each port will be provided with two LEDs indicating link status, simplifying network debugging.
Peripheral Interfaces
The following peripheral interfaces are provided for expanding the capabilities of the school server.
USB 2.0
At least six Universal Serial Bus (USB) 2.0 interfaces should be provided for extending the storage and communication capabilities of a School server.
This assumes that up to three external ports will be used for Active Antenna, another for an external CD/DVD RW, another for a possible WAN connection, and one last one for temporary USB key or external USB drive attachment.
The total amount of power consumed by the USB devices will be clamped to 2.5 A at 5 Volts (12.5 W) total, aggregrated across all devices. Any single device may pull up to 1.5 A (7.5 W).
PCI-Express Slot
A short, full height PCI-Express (4 channel) expansion slot is provided internally in the XS. This slot is intended for the addition of a DVB-S receiver and demodulator, but may be used for other purposes as well.
The power consumption of this expansion slot limited to 15 W. Exceeding this will lower the maximum ambient operating temperature of the server, and may also prevent the use of a second disk drive.
Non-Volatile Storage
to consider : how many drives are recommended for backups and replacement? with only 1 drive, what is the path to recovering a dead/dying drive? this may depend on quality of connection between server and upstream backup at a regional center
Internal Disk Drive
One internal 3.5 in. disk drive will be provided. The disk interface will be SATA (version 1 or 2). The capacity of this disk drive WILL vary, with a minimum size of 300 GB at this time.
A second 3.5 in. disk drive will be supported in the XS, primarily for onsite drive replacement, but also allowing storage expansion. Use of a second disk drive will significantly increase the power consumption of the server.
A fan-less aluminum disk drive cooler may be worthwhile as a prevention of overheating measure.
External Disk Drives
Additional disks may be added using the external USB 2.0 ports.
Flash
A fair amount (512 MB) of NAND Flash (solid state non-volatile) memory will be provided on the XS server to allow the operating system and minimal services to continue operation even though the primary disk drive has failed.
A smaller amount (512KB) of NOR Flash will be provided for storage of configuration information and boot firmware.
On OTS systems Flash storage is currently not needed - or used. If you can obtain flash disks for all your OTS XS machines, do discuss it in the mailing list - it is an extremely valuable addition.we are considering using adding USB keys or SD cards to allow similar functionality.
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 (30W 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
Temperature
The school server should meet the same environmental specifications for temperature as the laptop. This is 50 C ambient.
Water, Dust, and Salt Fog
The server should be resistant to water spray from all directions, but does not have to survive immersion. It should be capable of long-term operation in a constantly humid (100%) environment, with salt fog and dust.
While the server will contain fans, they will externally accessible for easy replacement and under software control to conserve power.
Connectors and buttons should be resistant to water and dust intrusion. Buttons should be sealed against water, and connectors located and cables dressed to prevent water intrusion.
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 optional/modular UPS...
Drop and Shake
The school server should meet higher drop and shake specifications than standard consumer desktop PCs, to account for rough transport in the delivery.
XSX Specifications
OTS systems builders should aim for these XSX specs:
- 1GHz+ x86 processor
- 1+ GB main memory
- Four to six USB interfaces, with power for three Marvell Wifi nodes and an external disk drive.
- One 300GB+ 3.5in SATA drive (500 GB makes more sense right now)
- Power and space for a second disk drive
- Two 100baseT network interfaces (one will do in some cases)
- Minimal fans
- replace them with heatsinks where possible
- easily replaceable
- Minimal openings in the case to avoid dust, etc
- Test it in the heat - should work in up to 50 deg C
- Test the actual network performance
There are many hardware platforms meeting these specifications. We are working on a recommendation for a low power version.