Rackmount Basics

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Rackmount Basics
By Gene Lee July, 2002
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Introduction
This presentation is designed to provide basic
knowledge of rackmount specifications, as well as
demonstrations on the installations of some of
the commonly used accessories. Although we try
to cover all topics related to rackmount computer
chassis, please feel free to contact us should
you come across anything that you might need more
assistance on. The information given in the
following sections is based on the EIA-RS-310
rackmount equipment specifications.
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Types of Equipments
Cabinet Cabinet is usually refer to a
freestanding and self-supporting enclosure for
housing electrical and or electronic equipment.
It is usually fitted with doors and/or side
panels, which may or may not be removable. A
cabinet shall be standard when it conforms to the
dimensional requirements.
17.72 (450mm) min Inside width
42U U1.75
18.3 (465mm )min Hole center to center
19 min Ear to ear outside
dimension
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An equipment or chassis in a typical cabinet can
be mounted fix by ways of using front mounting
ears plus rear supporting brackets. One can also
place an equipment on angle supports or
cantilever shelves as well. However, the most
common way to mount rackmount computer or storage
subsystems is by sliding rails. Below photo
shows 20 and 26 ball bearing rails with
quick-detach feature, AIC part number SR-20 (20)
and SR-26 (26).
The advantage of using slide rails is to allow
unit to be easily pulled out of cabinet for
maintenance. Also for heavier equipment mounting
is easier with sliding rails, without having to
hold on to the unit when mounting. Photo to the
right shows a 1U and a 2U chassis with
ball-bearing rails.
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Rack Rack is generally referred to the two-post
style open-frame type as opposed to the four-post
enclosed cabinet design. Rack could be with or
without casters. Since it has only two mounting
posts, equipments are typically mounted by the
front ears along, or by the center-mount brackets
if the depth and weight of the chassis requires a
more balanced mounting position. Cantilever
shelves are also widely used. It is also
referred to as Telco Rack, since it is widely
used in the telecommunication industry to mount
telephone relays. To the right is a photo of a
35U open frame rack with casters, AIC Part
Number RACK-35U-OP
Cantilever Shelf
Center Mount
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Rackmount Computer Chassis
People often have questions on what can be used
in a rackmount computer chassis. Years ago only
single-board computer (SBC) along with passive
backplane were used in rackmount computer
chassis. They were mostly used to control
machinery(automation), acquire data, or for
telecommunication applications (PBX). However,
due to the coming of the Internet era,
requirements to house large numbers of
co-location servers drove the market to select
something much more compact and easier to manage.
As a result many of the desktop servers got
transformed to the slim and rack mountable metal
enclosures. The space required for four desktop
servers can easily house 40 rackmount chassis in
a cabinet. The rackmount computer chassis we are
seeing today is nothing more than a desktop
computer case with mounting ears and rails.
Having said that, it is definitely a much tougher
task trying to pack same amount of components
into a slimmer environment. We will try to cover
the characteristics of each size of rackmount
computer chassis in the following few sections.
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How to Select the Right Chassis
There are three important factors that determine
which chassis to use 1)Size of the
motherboard There are basically the following
different standard sizes available today
9 x 7.5 Flex ATX

• Mini Flex ATX
• Flex ATX
• Micro ATX
• ATX
• Extended ATX
• SSI EEB V. 3.0
• SSI MEB 16 x 13

12 x 9.6 ATX
7 x 7 Mini Flex ATX
9.6
7.5
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9.6 x 9.6 Micro ATX
12 x 13 Extended ATX or SSI EEB 3.0
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9.6
13
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How to Select the Right Chassis continued
In general anything thats longer than the ATX
size of 12 x 9.6 will need to go into an
extended chassis thats at least 25 or more in
depth. Some motherboards that are slightly
longer at 10.5 will mostly likely fit in a
shorter chassis at 21 of depth. As for SSI MEB
standard of 16 x 13, AICs RMC4L-S4520 chassis
is designed specially for Tyans S4520 quad Xeon
server board that comes in this form factor. 2)
CPU Speed Its important to know whether a single
or dual CPU based motherboard is going to be
used. Among the dual CPUs, its also important
to know whether its for Intel Tualatin, Xeon
Prestonia, or AMD Athlon MP. Different chassis
has different cooling design, especially in 1U
where space is tight and fans are limited in
size. The following chart demonstrates a
Thermal Scale based on the available CPUs on
the market today.
M o r e F a n s N e e d e d
Celeron Tualatin
Dual Tualatin
Dual Xeon
Dual Athlon
P4
Athlon
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How to Select the Right Chassis continued
When selecting the appropriate chassis for the
processors, please also make sure to select
recommended CPU coolers. After all, cooling
cannot be done on the chassis along. 3) Capacity
expansion slots and drive bays The last
question you should ask yourself is what about
expansion slots and drive bays? Typically 1U
can take one expansion slot and the most two, and
2U can most likely get you two to three depending
on the motherboards. When you need more than
three expansions, or when all expansion slots
need to be at different bus clocks and voltages,
then 3U and higher where direct expansions are
available will be your choice. Drive bay
arrangements vary from single HDD with slim
CD-ROM to sixteen hot-swappable drive bays with
slim CD and FDD bays. Please make sure to always
leave yourselves room to grow when selecting
drive bay configurations. When choosing SCSI
hot-swap option please make sure to use HDD with
80-pin SCA2 connector. For IDE hot-swap option,
AIC has a patent-pending adjustable backplane
design that will accommodate all brands of IDE
HDDs without using ribbon cable adapter.
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How to Select the Right Chassis Example
Here is typically how the chassis selection
process begin Application Requirements - Please
remember that a product always starts with
application, not from the chassis or motherboard
Customer needs to build an email server for a
small office of 10 people. He is looking at a
dual PIII/Tualatin board from Tyan S2518UGN
with SCSI controller onboard along with two 1.13
GHz Intel Tualatin processors and 256MB memory.
He will also need to run two 60GB Ultra-160 HDDs
in mirroring, one CD-ROM and FDD, and one PCI
Gbit Ethernet card for bandwidth. Step 1 check
motherboard size This is a 12(W) x 9.6 (D)
standard ATX server board. Therefore, we can use
either long or short chassis. Step 2 check CPU
type Dual Tualatin configuration does not
require a whole lot of cooling efforts.
Therefore, we do not need to choose chassis
optimized for P4, Xeon, or Athlon
processors. Step 3 check expansions Since
customer only needs two SCSI HDDs and one PCI
expansion, we can select one 1U chassis with at
least two hot-swap SCSI HDD bays and sufficient
cooling for dual PIII. Conclusion - RMC1M has
dual SCSI hot-swap bays, slim CD and FDD bays,
and has six cooling fans, and since S2518 uses 25
degree slanted DIMM sockets cooling should not be
a challenge. If customer is not comfortable with
1U chassis, the closest 2U chassis we can select
is either RMC2M with 4 hot-swap bays, or RMC2N
with 4 x 5.25 bays and use BR-SCA23 for
hot-swap bay conversions.
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1U Chassis Basics
1U chassis is the toughest to build due to many
size limitations. Although 1U is defined as
1.75(44.45mm) high, the maximum height of the
chassis is actually at around 44mm which is
approximately 1.732, leaving just about 0.45mm
of clearance between every two 1U boxes. With
the sheet metal thickness at 1.2mm at top and
bottom, we are left with only about 1.64 of net
height for everything that needs to go into this
box.
1.2mm
44mm
41.6mm 1.64
40mm Fan
As a result, the maximum height of any component
that needs to fit in a 1U is at 1.6. A
full-size CD-ROM drive and a full-height HDD are
all at 1.6 high. To allow better air flow, a
slim CD-ROM drive and 1 HDD are usually
preferred.
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1U Chassis Basics- continued
Also due to the height limitation, low-profile
CPU coolers must be used in 1U. Preferably
copper heat sink based CPU coolers are used for
much needed thermal characteristics. A
right-angle riser card must be used to provide
expansion slot in 1U as well.
1U low-profile Copper heat sink CPU cooler AIC
Part CPU-P4-FAN
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1U Chassis - Expansions
1U chassis with its low-profile form factor
provides space-saving advantage over bigger
chassis. In ISPs co-location data center where
monthly charge is based on the amount of space
occupied, 1U is often the choice of many.
Although cost of 1U chassis and associated
components typically are higher than that of 2U
and above, the monthly savings should pay for
the higher initial costs in no time. The
disadvantages of 1U chassis are expandability and
thermal. Majority of 1U chassis can provide only
one PCI expansion slot. However, AIC has many 1U
chassis that can provide two expansion slots.
Here is a closer look at RMC1N-XP chassis.
1
2
1
2
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1U Chassis - Cooling
Thermal in 1U chassis has always been an issue
for many people. The newest technologies for
cooling fans and blowers adopted by AIC along
with some proprietary innovative designs enabled
us to conquered the toughest cooling challenges
to date. AICs patent-pending air-intake air
duct along with powerful exhaust fans provide the
best cooling solution on the market today.
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2U Chassis Basics
.
As you can see 2U chassis has much more room to
work with, therefore, it does not have as big of
a challenge on cooling as 1U. 2U also has more
expansion capabilities.
1.2mm
8CM Fan
Power supply
88mm
Low-profile slots without riser card
3 full-height expansions via 3-slot PCI riser card
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2U Chassis Riser Cards
.
Many people have questions on how to use riser
card. Riser card is merely acting as an
extension to the onboard PCI slots. There are
basically two types of riser cards available.
Active uses PCI bridge on the riser card
itself to provide IRQ signals Passive uses
paddle boards to transfer IRQ signals from other
slots off the motherboard. Due to the
specifications of PCI slot, each slot only
carries one IRQ signal. Therefore, when putting
three cards into one slot the additional two IRQ
signals must be routed from other onboard PCI
slots. AIC provides passive riser cards with
paddle boards for cost-competitiveness reasons.
Photo to the right shows RC2-017 riser card with
2 x 64-bit PCI plus AGP Pro slots. This is a
combo card where two distinct cards are
combined into one providing connections from two
different sources with different bus clock and
voltages.
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2U Chassis Riser Cards - continued
.
Determining which motherboard is suitable to use
which riser card is not as difficult as many
think. Below is a standard ATX motherboard from
Intel SAI2. The circled mounting hole in the
picture is on every motherboard, and can be used
to determine whether this board has the right
slot locations for riser cards or not.
1
This mounting hole is the one immediately
following the onboard I/O ports. Approximately
1 to the left of this mount hole is typically
referred to as 6 or 2 slot, depending whether
1 slot is marked as the last one on the left or
the one right behind this mounting hole. In
either case, if this is a PCI slot you will have
no problem using a standard riser card. For the
case where this slot is either an AGP or missing
completely, you would need to use an offset
riser card for PCI expansion, such as RC2-011
(32-bit with ribbon bridge) or RC2-016 (64-bit
with PCB bridge) riser cards.
Onboard I/O ports
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2U Riser Card Types
Below diagrams show the three major types of
riser cards that AIC offers for 2U chassis.
Riser Card Mounting Plane Cannot Change
No Connection Ribbon Cable
AGP Slot Extension
AGP Slot
IRQ Paddle Boards
Basic Type- directly connected Example RC2-007
32 bit x 3 RC2-012 64 bit x 2
Offset type Example RC2-011 32 bit x 3 with
ribbon RC2-016 64 bit x 2 using PCB instead of
ribbon cable
Dual AGPPCI type Example RC2-013 32 bit x 2
AGP RC2-017 64-bit x 2 AGP Pro
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3U Chassis Basics
.
The significance of 3U chassis is that this form
factor is the smallest one can use without using
riser cards for full size PCI expansions.
However, there is still a height limit of 3.9 on
the expansion cards allowed due to physical
limitation of 3U form factor. Not needing riser
card also has another advantage, which is to
allow expansions of PCI-X slots with different
speeds. Some high speed AGP PRO video cards also
do not work well with riser cards due to signal
timing delays caused by riser cards.
1.2mm
3.9 Max
132.5 mm
8CM Fan
Power supply
3U chassis also offers significantly more drive
bays than 1U and 2U chassis.
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4U 7U Chassis
4U chassis basically is the closest to desktop
computer chassis in dimensions. For that reason
AICs RMC4S can also be configured as desktop or
mid-tower computer chassis. 4U can take pretty
much any desktop components, including PS/2 size
power supplies and full-size CD-ROM drives.
Also, 4U can take 120mm fans for high air-volume
cooling. 5U is just a height-extension of 4U with
one extra U of space for additional drive bays.
The extended 5U chassis is often the popular
choice for telecommunication industry with 20
slot expansions and large capacity redundant
power supply options. 7U chassis is designed to
use height to exchange for depth. For customer
that needs the capacity 5U extended chassis
offers yet has a 20 deep cabinet, 7U is the
perfect choice with double-deck design.
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Hot-Swap Backplane
This section is designed to give some graphic
illustrations on how to connect IDE and SCSI
backplane. IDE There is really no standard way
to make an IDE HDD hot-swappable (or warm-swap).
Since data and power on the IDE HDD comes from
two different connectors, one needs to combine
them to make one single hot-swappable connection.
AIC uses a 48-pin connector to combine the 4-pin
power with the 40-pin data connectors.
Since the data connector is fixed and is located
differently from brand to brand, we use a
patent-pending design that allows up to 3mm of
adjustable lateral space to match with any drive
without using flexible ribbon cable.
Hard Disk Drive
Tray Mid-Plane
backplane
IDE HDDs can be connected either with two
devices per channel, I.e., Master Slave, or
Master only with one HDD per cable. To do
hot-swap it is recommended to use only a single
Master drive per cable.
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IDE - continued
When using a typical two-channel IDE controller
or RAID controller without hot-swap, the cables
are connected as follows
ATA 100 HBA or motherboard onboard controller
Channel 2
Channel 1
Master 2
Slave 2
Master 1
Slave 1
This is the ideal setup for RMC1F chassis with
four internal HDD bays.
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IDE - continued
When using a typical four-channel IDE RAID
controller with hot-swap support, the cables are
connected as follows
ATA 100 IDE RAID Controller
RMC1Q is ideal for this kind of setup but with
only three hot-swap IDE HDDs. For RMC4D-IDE
chassis user can use two 8-channel IDE RAID
controllers to support sixteen Master HDDs. It
is recommended to use round cables for easier
cable-routing and better air flow.
Channel 1
Channel 2
Channel 3
Channel 4
Master 1
Master 2
Master 3
Master 4
RAID 0 - striping
RAID 1 - Mirroring
RAID 5 striping with parity
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SCSI Backplane
When choosing a chassis with SCSI hot-swap bays
please use SCSI HDDs with SCA2 80-pin connector,
which consists of 68-pin of data plus grounding
and power. The power pins are made slightly
longer, so that when disengaging the HDD from
backplane, data pins would be disconnected first
while power pins are still connected for split of
a second. This standard design enables a safe
hot-swap interface for the hard disk drives. SCSI
devices can be daisy-chained, and each channel
can support up to 15 devices. Therefore, when
using a dual-channel controller one can select to
run all the attached devices all in one single
channel, or split into dual channels for
mirroring or better performance. Below shows how
RMC1Q-SCSI chassis can be configured with a
single cable.
HDD 3
HDD 2
HDD 1
To HBA
This configuration shows three single-bay SCSI
backplane daisy-chained with one single cable
with five connectors. Termination is done at the
end of the cable with a female terminator.
Female Terminator
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SCSI Backplane-continued
The following figures shows how RMC2Ds three
backplanes can be connected as single channel of
9 devices or dual channels of 3 6 devices.
HDD 1, 2, 3
HDD 4, 5, 6
HDD 7, 8, 9
OUT
OUT
OUT
male Terminator
IN
IN
IN
To HBA
Each backplane supports three HDDs and only link
cable is needed to connect every two backplane.
HDD 1, 2, 3
HDD 4, 5, 6
HDD 1, 2, 3
OUT
OUT
OUT
male Terminator
male Terminator
IN
IN
To HBA Channel 2
To HBA Channel 1
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SATA
Serial ATA is a new serial I/O technology that
utilizes point-to-point data transmission method
to get rid of the bus-arbitration and saturation
bottlenecks that typical parallel I/O devices
face. Therefore each HDD must be connected
directly to a dedicated channel on a controller
(HBA).
SATA RAID Controller
SATA also offers another advantage over PATA or
SCSI as you can see from the figure to the left,
the cable. Each SATA cable only has 7 wires as
opposed to 80 in the ATA100 cable. The smaller
cable makes cable-routing much easier, and thus
improve the air flow in low-profile chassis such
as RMC1D and 2E where high capacity drive bays
are designed
HDD 1
HDD 2
HDD 3
HDD 4
RAID 0 - striping
RAID 1 - Mirroring
RAID 5 striping with parity