Abstract:
The disclosed embodiments relate to a rack for housing electronic components with a movable power distribution unit (PDU). The rack includes a rack housing configured to accommodate a plurality of electronic components. It also includes a first PDU configured to supply electrical power to the plurality of electronic components. The rack additionally includes an attachment mechanism configured to movably attach the first PDU to the rack housing, so that the first PDU can be moved to create an access space to facilitate a maintenance operation while the first PDU continues to supply power to the plurality of electronic components.

Description:
RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 61/856,332, entitled “Electronics Rack with a Moveable Power Distribution Unit” by Jacob R. Rose, filed 19 Jul. 2013, the contents of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     1. Field 
     The disclosed embodiments relate to the design of an electronics rack for housing electronic components, such as server blades, storage devices, or network switches. More specifically, the disclosed embodiments relate to the design of an electronics rack with a movable power distribution unit (PDU), which can be moved to create an access space to service other components in the electronics rack. 
     2. Related Art 
     Perhaps the most significant development on the Internet in recent years has been the rapid proliferation of online social networks, such as LinkedIn® and Facebook®. Billions of users are presently accessing such social networks to connect with friends and acquaintances and to share personal and professional information. In order to handle this large volume of traffic, these online social networks are increasingly relying on enterprise computer systems to run their websites. A failure of one of these enterprise computing systems can be disastrous, potentially resulting in millions of dollars in lost revenue. More importantly, a failure can undermine user satisfaction, making users less likely to access a particular online social network. Hence, it is critically important to ensure high availability of such enterprise computing systems. 
     These enterprise computer systems are typically mounted in racks housed in data centers. To ensure continuous functioning of the enterprise computer systems, each rack typically includes multiple power distribution units (PDUs) that supply power to the electronic components in the rack. In this way, when one of the PDUs fails, the electronic components will continue to receive power from another PDU in the rack. 
     However, replacing a failed PDU can be pose problems. Note that space is at a premium inside a rack, so the multiple PDUs are typically located in close proximity to each other. Unfortunately, this close proximity and the large number of power cables that connect the PDUs to the electronic components in a rack often makes it impossible to replace a failed PDU without powering down the entire rack. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates a rack for housing electronic components in accordance with the disclosed embodiments. 
         FIG. 2A  illustrates a rack that contains two PDUs including an inner PDU and an outer PDU in accordance with the disclosed embodiments. 
         FIG. 2B  illustrates how the outer PDU can be moved to facilitate replacing the inner PDU in accordance with the disclosed embodiments. 
         FIG. 3A  presents a frontal view of a sliding bracket in accordance with the disclosed embodiments. 
         FIG. 3B  presents a side view of the sliding bracket in accordance with the disclosed embodiments. 
         FIG. 3C  presents an orthographic view of the sliding bracket in accordance with the disclosed embodiments. 
         FIG. 3D  presents another orthographic view of the sliding bracket in accordance with the disclosed embodiments. 
         FIG. 3E  presents a top view of the sliding bracket in accordance with the disclosed embodiments. 
         FIG. 4  presents a flow chart illustrating the process of replacing a failed inner PDU in accordance with the disclosed embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable any person skilled in the art to make and use the present embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present embodiments. Thus, the present embodiments are not limited to the embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. 
     The data structures and code described in this detailed description are typically stored on a computer-readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. The computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing computer-readable media now known or later developed. 
     The methods and processes described in the detailed description section can be embodied as code and/or data, which can be stored in a computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the computer-readable storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the computer-readable storage medium. Furthermore, the methods and processes described below can be included in hardware modules. For example, the hardware modules can include, but are not limited to, application-specific integrated circuit (ASIC) chips, field-programmable gate arrays (FPGAs), and other programmable-logic devices now known or later developed. When the hardware modules are activated, the hardware modules perform the methods and processes included within the hardware modules. 
     Rack Structure 
       FIG. 1  illustrates the structure of an exemplary rack  100 , which is configured to house electronic components in accordance with the disclosed embodiments. As illustrated in  FIG. 1 , rack  100  includes a rack housing  101 , which is configured to accommodate a number of electronic components  102 , such as server blades. In general, rack  100  can house any type of electronic component, including but not limited to: server blades; networking components; storage devices; and telecommunications components. 
     Rack housing  101  includes a door  107 , which can be opened to provide access to the connectors for the electronic components. These connectors provide power and other types of connections for the electronic components, such as network connections and connections between the electronic components in the rack. 
     Rack  100  also includes a number of PDUs  103 - 106 , including two PDUs  103 - 104  located on the left-hand side of rack housing  101  and two PDUs  105 - 106  located on the right-hand side of rack housing  101 . Although the exemplary rack  100  illustrated in  FIG. 1  includes four PDUs  103 - 106 , in other embodiments, rack  100  includes only two PDUs  103 - 104 , and the other PDUs  105 - 106  can be replaced with communication lines or other circuitry. 
     As illustrated in  FIG. 1 , a given PDU  105  includes a number of black electrical outlets for supplying power to the plurality of computer system components, and also includes circuit breakers  108 - 111  for the electrical outlets. 
     Note that PDUs  103 - 106  connect to external power through power cables  115  that pass through an opening in the bottom of rack housing  101 . In an alternative embodiment, power cables  115  connect to external power through an opening in the top of rack housing  101 . 
     Movable PDU 
       FIGS. 2A and 2B  illustrate a moveable PDU in accordance with the disclosed embodiments. More specifically,  FIG. 2A  illustrates a top-down view of the inside of rack housing  101 . Note that rack housing  101  contains two PDUs, including an inner PDU  202 , which is connected to components  102  through a first set of power cables  216 , and an outer PDU  204 , which is connected to components  102  through a second set of power cables  218 . 
     Note that PDUs  202  and  204  are connected to rack housing  101  in different ways. In particular, inner PDU  202  is connected to a fixed bracket  214  which is affixed to rack housing  101 . In contrast, outer PDU  204  is connected to a sliding bracket  210 , which is slidably mounted to a post  208  (also referred to as a “rail”) that is affixed to rack housing  101 . (Note that sliding bracket  210  is mounted on two posts  208 , one of which is connected to the top of sliding bracket  210 , and the other of which is connected to the bottom of sliding bracket  210 .) 
     When sliding bracket  210  is located in a normal-operating position as illustrated in  FIG. 2A , a fastener  212  can be used to lock sliding bracket  210  so that sliding bracket  210  does not move along post  208 . 
     Note that if outer PDU  204  fails, outer PDU  204  can be easily replaced without having to power down the electronic components  102  within rack  100  because other system components do not obstruct the replacement. For example, replacing outer PDU  204  can involve the following operations. First, external power is removed from outer PDU  204  and cables  218  are disconnected from outer PDU  204 . Next, outer PDU  204  is replaced with a new outer PDU  204  and the cables  218  are connected to the new outer PDU  204 . Finally, external power is connected to the new outer PDU  204 . 
     In contrast, when inner PDU  202  fails, inner PDU  202  is harder to replace because outer PDU  204  and its associated power cables  218  are in the way. Fortunately, sliding bracket  210  enables outer PDU  204  to be moved to facilitate replacing inner PDU  202  as is illustrated in  FIG. 2B . More specifically, when inner PDU  202  fails, inner PDU  202  can be replaced by performing the following operations. First, external power is removed from inner PDU  202 . Next, cables  216  are disconnected from inner PDU  202 . Then, fastener  212  is unhitched and sliding bracket  210  is moved to the end of post  208 . This creates an access space  206 . Inner PDU  202  is then replaced with a new inner PDU  202  through access space  206 . Finally, cables  216  are connected to the new inner PDU  202  before external power is connected to the new inner PDU  202 . 
     Note that if outer PDU  204  were not movable, it would be necessary to remove outer PDU  204  (and to disconnect associated cables  218 ) to replace a failed inner PDU  202 . Moreover, removing outer PDU  204  and disconnecting cables  218  requires the entire rack  100  to be powered down, which can cause problems if critical applications are running in rack  100 . 
     Sliding Bracket 
       FIGS. 3A-3E  present a number of views of sliding bracket  210  and associated mounting structures in accordance with the disclosed embodiments. More specifically,  FIG. 3A  presents a frontal view of sliding bracket  210 ,  FIG. 3B  presents a side view,  FIG. 3C  presents a first orthographic view,  FIG. 3D  presents a second orthographic view, and finally  FIG. 3E  presents a top view. Referring to  FIG. 3A , note that sliding bracket  210  includes rows of holes  304  which can be used to mount PDU  204 . Moreover, as mentioned above, sliding bracket  210  is mounted on two posts  208 , one of which is connected to the top of sliding bracket  210 , and the other of which is connected to the bottom of sliding bracket  210 . In the embodiment illustrated in  FIGS. 3A-3E , post  208  is affixed to a mount  302  which is attached to rack housing  101 . Note that there are two such mounts  302 , one of which is connected to the post  208  at the top of sliding bracket  210 , and the other of which is connected to the post  208  at the bottom of sliding bracket  210 . 
     As illustrated in  FIG. 3E , mount  302  also includes an extension  306  that holds a fastener  212 . Fastener  212  is configured to lock sliding bracket  210  in place when sliding bracket  210  is flush with mount  302 . When sliding bracket  210  is locked in this position, the attached PDU  204  is in a normal-operating position. 
     Note that a large number of possible ways exist to fixedly attach a PDU to a rack housing to facilitate moving the PDU to perform system maintenance operations. In general, any type of movable mounting system or mechanical linkage can be used, and the disclosed embodiments are not meant to be limited to slidable mounting systems. For example, instead of the slidable mounting system, a hinged mounting system can be used. 
     Process of Replacing a Failed Inner PDU 
       FIG. 4  presents a flow chart illustrating the process of replacing a failed inner PDU in accordance with the disclosed embodiments. Referring to the embodiment illustrated in  FIGS. 2A and 2B , at the start of the process, the system detects a failure of the inner PDU  202  (step  402 ). 
     Next, in order to replace the failed inner PDU  202 , external power is first removed from inner PDU  202  (step  404 ). Then, the power cables  216  that are used to supply power to components in rack  100  are unplugged from inner PDU  202  (step  406 ). Next, fastener  212  is unfastened, and outer PDU  204  is moved by sliding it along posts  208  to create an access space  206  for inner PDU  202  (step  408 ). (Note that power cables  216  can alternatively be unplugged after outer PDU  204  is moved.) 
     Inner PDU  202  is then unfastened from bracket  214  and is removed from rack housing  101  though access space  206  (step  410 ). Then, a new inner PDU  202  is inserted into rack housing  101  through access space  206  and is fastened to bracket  214  (step  412 ). 
     Outer PDU  204  is then moved back into place by sliding it along posts  208  and is fastened in place by fastener  212  (step  414 ). Next, power cables  216  are plugged into new inner PDU  202 . (Note that power cables  216  can alternatively be plugged into new inner PDU  202  before outer PDU  204  is moved back into place.) Finally, external power is connected to new inner PDU  202  (step  418 ). 
     Extensions 
     The ability to move a PDU without having to power down the associated rack can be used to facilitate other system maintenance operations besides replacing a failed inner PDU. For example, the PDU can be moved to enable a service technician to “repair” a failed inner PDU instead of replacing the failed inner PDU. Also, the PDU can be moved to enable a service technician to access other system components and wires located behind the PDU. For example, the PDU can be moved to enable a service technician to replace a network cable located between the PDU and electronic components in the rack. 
     Also, the PDU can be moved in a number of different ways and is not meant to be limited to the sliding movement for the exemplary configuration illustrated in  FIGS. 2A-2B . For example, the PDU can be attached to the rack housing a hinge, which allows the PDU to move in a swinging motion. Alternatively, the PDU can be attached to the rack housing through a mechanical linkage that allows the PDU to be moved translationally and/or rotationally to facilitate the maintenance operation. 
     Note that this translational movement can generally be in any direction: up, down, forward, backward, right or left. Similarly, the rotational movement can be clockwise or counter-clockwise around an axis that is oriented in any direction. 
     Alternatively, the PDU can be mounted to the rack housing in a manner which makes it easy to “completely disconnect” and move the PDU from its normal-operating position in the rack housing to create an access space without disconnecting the power cables that connect the PDU to the electronic components in the rack. 
     The PDUs can also be mounted in different locations and orientations within the rack housing. In the embodiments illustrated in  FIGS. 1 ,  2 A and  2 B, the PDUs are mounted along the inside of the side panels of the rack housing, and the PDUs are oriented to run from the top to the bottom of the rack housing. However, in other embodiments, the PDUs can be mounted near the front or the back of the rack housing, or near the bottom or the top of the rack housing, as long as the power cables for the PDUs can reach the electronic components in the rack housing. The PDUs can also be oriented in any direction, top-to-bottom, side-to-side, or front-to-back, within the PDU (as long as the power cables can reach the electronic components). 
     The foregoing descriptions of embodiments have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present description to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present description. The scope of the present description is defined by the appended claims.