Ventilated backplane for mounting disk drives in computer systems

An improved cooling system for a computer system includes a ventilated backplane for a disk drive cage. The backplane is rigidly secured to the rear of the disk drive cage and includes a plurality of apertures therein to permit convective heat transfer between the inner cavity of the drive cage and the main enclosure of the computer system. A fan assembly is attached to the backplane on the side opposite the drive cage to further enhance heat transfer through the ventilation apertures. In one embodiment, the fan assembly includes a plenum attached to the backplane and a fan attached to the plenum. In another embodiment, a fan housing is attached to the backplane and incorporates one or more fans therein.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to cooling of disk drives within a computer, 
and, more particularly, to an apparatus and method for ventilating a disk 
drive cage using apertures in a backplane. 
2. Description of the Related Art 
Modem computers often include multiple hard-disk drives, flexible-disk 
drives, CD-ROM drives, and the like. These drives include motors and 
mechanisms for spinning the storage media and for moving read heads or 
read/write heads, and also include circuitry for controlling mechanical 
movement as well as the transfer of data. For example, a computer system 
may include a RAID (Redundant Array of Inexpensive Disks) subsystem which 
includes three or more hard-disk drives. 
In computer systems having RAID subsystems, the disk drives are mounted on 
separate frames or trays and inserted side-by-side into a cavity within 
the computer. The internal sheet metal chassis of the computer defines 
guides for aligning connectors on the drives with mating connectors on a 
rigid backplane. The backplane defines an inner wall of the cavity and 
provides electrical interconnections to and from the mating connectors. 
The backplane may be a passive backplane, or it may include electronic 
components which transfer data to and from the disk drives and which 
control the disk drives. 
Typically, the backplane is constructed of an insulating rigid substrate 
having the electrical connections formed on one or more layers. The 
backplane is firmly attached to the internal chassis of the computer, 
typically with threaded fasteners. The cavity defined on the sides by 
sheet metal panels of the internal chassis and on the inner wall by the 
backplane, is termed the "drive cage." 
Typically, a computer system having a RAID subsystem has a so-called 
"tower" configuration wherein the computer system is taller than it is 
wide, as opposed to a desktop system which is generally wider than it is 
tall. One aspect of a RAID subsystem is that a disk drive can be readily 
replaced if it fails during operation. Thus, a RAID subsystem is typically 
mounted in the computer system so that the disk drives can be extracted 
and inserted through the front of the computer system cabinet. In order to 
accommodate this feature, the backplane for the RAID subsystem is mounted 
with the backplane perpendicular to the side walls of the computer system. 
Due to the enclosed nature of the drive cage and the heat-generating drives 
within, this region is particularly difficult to cool. Indeed, much energy 
and resources have been expended in attempts to effectively cool the 
environment within the drive cage. Given enough room, fans can be 
installed at various locations surrounding the drive cage. For example, 
fans can be mounted within spaces surrounding the sides of the drive cage 
within the outer computer cabinet. Alternatively, external fans may draw 
air from, or blow air into, the drive cage from the exterior of the 
computer. All of these arrangements introduce trade-offs in space 
required, added weight, etc. Moreover, the enclosed box configuration of 
the drive cage limits the efficiency of any cooling arrangement, with the 
result that the temperature within the drive cage is often only slightly 
below that which would damage the fragile drive mechanisms, especially 
when operated over extended periods. 
Accordingly, there is a need for an improved apparatus and method for 
ventilating a disk drive cage, which is both efficient in cooling the cage 
and less obtrusive than prior designs. 
SUMMARY OF THE INVENTION 
One aspect of the present invention, is an electronic system having 
improved cooling for subsystems therein. The electronic system comprises 
an enclosure and a chassis within the enclosure. A backplane is mounted to 
the chassis within the enclosure. The backplane is planar and has a first 
side and a second side wherein the second side is opposite the first side. 
The backplane has a plurality of slots formed therein to provide a 
plurality of open passages from the first side to the second side. A 
plurality of electrical connectors are positioned on the first side of the 
backplane. The backplane provides electrical interconnections to and from 
the electrical connectors. A plurality of subsystems are plugged into the 
electrical connectors. The plurality of subsystems are mounted generally 
perpendicular to the first side of the backplane with each subsystem 
spaced apart from adjacent subsystems. At least one fan is mounted 
proximate to the second side of the backplane. The subsystems generate 
heat and the fan operates to move air through the open passages and 
between the subsystems, thereby cooling the subsystems. 
Another aspect of the present invention is backplane for an electronic 
system having a plurality of subsystems. The backplane comprises a first 
generally planar side and a second generally planar side with the second 
side opposite the first side. A plurality of openings are formed in the 
backplane between the first side and the second side. The openings permit 
air to flow through the backplane between the first side and the second 
side. A plurality of connectors are positioned on the first side to 
receive a plurality of subsystems. The connectors are spaced apart such 
that air flowing through the openings flows between the subsystems to 
thereby remove heat from the subsystems. Preferably, the backplane 
includes a fan mounted proximate to the second side of the backplane. The 
fan operates to move air through the openings to cause the air to flow 
between the subsystems. Also preferably, a plenum is included which covers 
the backplane. The fan is mounted to the plenum to move air through the 
plenum and through the openings in the backplane. Preferably, the plenum 
is mounted to the backplane. In one embodiment, the backplane includes a 
plurality of slots and the plenum has a plurality of tabs positioned to 
engage the slots to mount the plenum onto the backplane. Alternatively, 
the plenum is screwed to the chassis through the backplane. 
Another aspect of the present invention is a ventilated backplane for an 
electronic system. The vented backplane comprises a generally planar 
substrate material having first and second opposed sides. At least one of 
the first and second sides has a plurality of connectors mounted thereon. 
A plurality of openings are formed in the backplane between the first and 
second sides to permit air to flow through the backplane. 
Another aspect of the present invention is a method for cooling an 
electronic subsystem. The method comprises the step of mounting the 
components of the electronic subsystem in a subsystem enclosure having a 
backplane at one end thereof. The backplane provides electrical 
interconnections to the subsystem. The backplane has a plurality of 
apertures formed therein. The method comprises the further step of moving 
air through the apertures in the backplane to cool the components of the 
electronic subsystem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates an exemplary computer system 20 into which the present 
invention can be incorporated. The computer system 20 may be of a variety 
of types, but in the present example is shown as a server system which 
features a plurality of hard disk drives configured as a RAID system and 
farther includes one or more floppy drives, CD ROM drives, tape drives, 
and the like. As illustrated, the computer system 20 is preferably 
enclosed within a so-called "tower" enclosure or cabinet, which has a 
height greater than the width of the front thereof and which further has a 
depth greater than the width of the front. The computer system 20 includes 
a stylized front panel 22 having controls, indicators and access for one 
or more floppy disk drives, a CD ROM drive, etc. Further, the front panel 
22 may be opened to provide access to the disk drives of the RAID 
subsystem therein. 
On the larger left side of the computer system 20, a side door 24 is 
provided, which can be easily removed. The computer system 20 is typically 
assembled such that components within the computer system 20 are easily 
accessible with the side door 24 removed. 
As illustrated in FIG. 2, the side door 24 of the computer system 20 has 
been removed to expose an inner sheet metal chassis 26. The computer 
system 20 includes a plurality of inner bracings and mounting structures 
for the various components. In FIG. 2, the stylized front panel 22 has 
also been removed to expose a planar front plate 28. The front plate 28 
includes a large rectangular opening 30 leading to one or more cavities 
defined within a drive cage 32. The drive cage 32 comprises side walls 34 
extending parallel to the side door 24, and a plurality of transverse 
horizontal shelves 36 provided with guides 38. The guides 38 extend from 
the opening 30 inward and are sized to receive tray assemblies 40 for hard 
disk drives 42. More particularly, the disk drives 42 are mounted to the 
tray assemblies 40, which are vertically orientated and which slide along 
opposed guides 38 into the cavity defined within the drive cage 32. Each 
tray assembly 40 includes a front pivoting bezel 44 having a handle 46 
therein. The configuration of the tray assembly 40 may be varied, but 
typically the bezel includes a lever-type latch which assists in inserting 
and removing the tray assembly 40 from the drive cage 32. 
As illustrated in both FIGS. 2 and 3, a connector 47 on the rear end of 
each tray assembly 40 aligns with a mating connector 48 provided on a 
first planar side 49a of a backplane 50. The disk drive 42 mounts to the 
tray assembly 40 in a conventional manner and is electrically connected 
therethrough to the connector 47, as is well known in the art. The 
backplane 50 defines an inner wall of the drive cage 32 and is securely 
fastened to the internal chassis 26. More particularly, the backplane 50 
includes a plurality of through holes 51 through which threaded fasteners 
52 mount into threaded holes within mounting brackets 54 of the chassis. 
One such fastener 52 is illustrated in FIG. 3, although there are 
preferably at least six--two each at the corners of the backplane 50 and 
two at the midpoint of the side edges. The fasteners 52 also ground the 
backplane 50 to the chassis 26. 
The backplane 50 is more clearly seen in FIGS. 3-5, and includes the first 
planar side 49a and a second, oppositely facing planar side 49b. The 
backplane 50 includes a plurality of apertures 56 which provide air 
passages therethrough to ventilate the drive cage 32. In the presently 
illustrated embodiment, the apertures 56 comprise two parallel columns of 
horizontally oriented slots 56 having rounded ends. Of course, other 
configurations of the apertures 56 are contemplated, the primary concern 
being avoiding the printed circuits on the backplane 50. The apertures 56 
greatly enhance the cooling capacity of fans disposed around the drive 
cage 32. More particularly, the apertures 56 augment currently existing 
cooling configurations for the drive cage 32 by enhancing convective heat 
transfer from the drive cage 32. Previous backplanes were solid plates 
which prevented convection heat flow through the inner wall of the drive 
cage 32. As previously discussed, this arrangement greatly decreased the 
efficiency of any cooling arrangement provided for the drive cage 32. 
Furthermore, the apertures 56 are located at the back of the drive cage 32 
so that air flow between the disk drives can pass straight out through the 
backplane 50. Previous cooling configurations in which fans were placed to 
the side of the drive cage 32 did not share this advantageous air flow 
location. 
To further enhance the cooling capacity of the apertures 56, a fan assembly 
is preferably attached to the backplane 50. In one embodiment, shown in 
FIGS. 6 and 7, the fan assembly 58 comprises a plenum 59 securely fastened 
to the backplane 50. The plenum 59 comprises a shallow box shape having 
four narrow sides 60 connected to a rear wall 61, with the opposite wall 
being open. The plenum 59 is mounted with the open wail juxtaposed against 
the backplane 50, as shown. A circular fan aperture 62 is formed in the 
rear wall 61 of the plenum. A fan 64 having a fan guard 66 rigidly 
attaches to the rear wall 61 at the fan aperture 62. 
To reduce vibration transmitted from the fan motor to the backplane 50, a 
pair of elongated foam strips 68 are placed between the plenum 59 and the 
backplane 50. One of the sides 60 of the plenum 59 includes a pair of 
hooks 70 adapted to fit within slots 72 formed in the backplane 50. The 
hooks 70 are formed in the side 60 of the plenum 59 furthest from the side 
door 24. Upper and lower tabs 74 extend from two of the other sides 60 at 
a location closer to the side door 24. The upper and lower tabs 74 receive 
threaded fasteners 76 that extend into threaded holes 77 within the 
backplane 50. The plenum 59 is thus relatively easy to install because the 
hooks 70 are positioned within the slots 72, and the fasteners 76 are 
simply inserted through the holes in the tab 74 and into the backplane 50. 
Likewise, removal of the plenum 59 is equally easy. The plenum 59 is 
further provided with a pair of outwardly extending flanges 78 that 
contact the foam strips 68. The flanges 78 compress the foam strips 68 
against the backplane 50 to reduce vibrations transmitted there between, 
and also to enhance a seal around the edges of connection between the 
plenum 59 and the backplane 50. 
The fan 64 can either pull air from the interior of the plenum 59 or push 
air therein. In either case, air is forced between the first and second 
planar sides 49a, 49b through the passages defined by the apertures 56 in 
the backplane 50. If air is being pulled from the plenum 59, the hot air 
generated by the disk drives 42 within the drive cage 32 is exhausted 
through the fan 64 into the cabinet of the computer 20, which typically 
has one or more other cooling fans in communication with the ambient 
atmosphere. Alternatively, if air is pushed into the plenum 59 by the fan 
64, cool air is forced into the drive cage 32, which then displaces the 
hot air there within through any of a plurality of vents surrounding the 
drive cage, such as for example, through vents in the front panel 22. 
Typically, the fan 64 runs continuously during operation of the computer 
system 20; however, the fan 64 may also be responsive to a temperature 
sensor (not shown) provided within the drive cage 32 to thereby operate 
only when the drive cage temperature exceeds a predetermined threshold. 
FIGS. 8-14 illustrate an alternative fan housing 82 which attaches to an 
alternative ventilated backplane 83, shown in FIG. 15. In the first fan 
assembly 58, the fan 64 was attached externally to the plenum 59. This 
arrangement is preferred if space within the computer system 20 is 
available because the efficiency of the fan is increased by the seals 
provided by attachment between the plenum 59 and the backplane 50. In some 
computer systems, however, space is limited. Thus, the alternative fan 
housing 82 may be used. 
The alternative fan housing 82 comprises a plurality of sides 84 and a rear 
wail 86. The rear wall 86 includes one or more fan grids 88, two of which 
are shown in FIGS. 8 and 12. To mount to the backplane 83, the fan housing 
82 is provided with a pair of outwardly extending hooks 90 on one side. 
The hooks 90 are adapted to fit within slots 92 in the backplane 83. The 
hooks 90 are provided on the side of the fan housing 82 away from the side 
door 24. On the opposite side, a pair of cantilevered latches 94, 
including outward detents 96, are provided. The latches 94 are sized to 
fit within slots 97 formed in the backplane 83. To install the fan housing 
82 onto the backplane 83, the hooks 90 are fitted within the slots 92, and 
the cantilevered latches 94 then snap into the slots 97. The outward 
detents 96 hold the fan housing 82 to the backplane 83, and the housing 
can be released by simply pressing the latches 94 inward. 
The alternative fan housing 82 has a lower profile than the first-described 
fan assembly 58 due to the mounting configuration of the fan within the 
housing 82. To secure the fan 64 within the housing 82, a plurality of 
locating pins 98 extend from an inner face of the rear wall 86. The fan 64 
is typically provided with holes for mating with the pins 98, and is 
pressed into the area between the sides 84 biasing apart a pair of 
cantilevered fan latches 100. The fan latches 100 include inward detents 
102 which retain the fan within the housing 82. 
As in the first embodiment of the fan assembly 58, the fan or fans 64 
either pull or push air through the ventilation apertures 56. A single fan 
64 may be provided within the housing 82, in which case one of the fan 
grids 88 shown in FIG. 8 is replaced with a solid wall. For the best 
cooling capacity, a pair of fans 64 are provided within the housing 82 and 
work continuously during operation of the computer system 20. 
Alternatively, the operation of the fans 64 may be triggered by a 
temperature sensor (not shown) within the drive cage 32. 
Although this invention has been described in terms of certain preferred 
embodiments, other embodiments that will be apparent to those of ordinary 
skill in the art are intended to be within the scope of this invention. 
Accordingly, the scope of the invention is intended to be defined by the 
claims that follow.