Patent Publication Number: US-8543789-B2

Title: System and method for managing a storage array

Description:
TECHNICAL FIELD 
     The present disclosure relates in general to data storage, and more particularly to a system and method for managing a storage array. 
     BACKGROUND 
     As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems. 
     Information handling systems often use an array of physical storage resources, such as a Redundant Array of Independent Disks (RAID), for example, for storing information. Arrays of physical storage resources typically utilize multiple disks to perform input and output operations and can be structured to provide redundancy which may increase fault tolerance. Other advantages of arrays of physical storage resources may be increased data integrity, throughput and/or capacity. In operation, one or more physical storage resources disposed in an array of physical storage resources may appear to an operating system as a single logical storage unit or “logical unit.” Implementations of physical storage resource arrays can range from a few physical storage resources disposed in a server chassis, to hundreds of physical storage resources disposed in one or more separate storage enclosures. 
     However, one downside of redundant storage arrays is that they generally require at least one physical storage resource within the storage array to serve as a redundant storage resource (e.g. for parity or mirroring). Thus, a redundant storage array typically consumes more power than a non-redundant storage array of similar storage capacity. 
     A traditional approach to reducing the power requirements of a redundant storage array includes powering down or spinning down one of the physical storage resources of the array. However, powering down one of the physical resources of a storage array may leave the storage array in a “degraded” state, whereby additional write operations to the array could become unrecoverable upon failure of one of the remaining powered-on physical storage resources, thus negating the original purpose of implementing the redundant array. 
     SUMMARY 
     In accordance with the teachings of the present disclosure, disadvantages and problems associated with power management in a redundant storage array have been substantially reduced or eliminated. 
     In accordance with an embodiment of the present disclosure, a method for managing a storage array is provided. The method may include segmenting each of a plurality of physical storage resources into a first storage area and a second storage area. The method may also include activating a first logical unit including each first storage area of the plurality of physical storage resources. The method may additionally include placing at least one designated physical resource of the plurality of physical storage resources in a powersave mode. The method may further include activating a second logical unit including the second storage areas of some of the plurality of physical storage resources but not the at least one designated physical storage resource. Moreover, the method may include storing data associated with a write operation intended for the at least one designated physical storage resource to the second logical unit. 
     In accordance with an embodiment of the present disclosure, a system for managing a storage array may include a plurality of physical storage resources and a device communicatively coupled to the plurality of storage resources. The device may be configured to segment each of the plurality of physical storage resources into a first storage area and a second storage area. The device may also be configured to activate a first logical unit including each first storage area of the plurality of physical storage resources. The device may additionally be configured to place at least one designated physical resource of the plurality of physical storage resources in a powersave mode. The device may further be configured to activate a second logical unit including the second storage areas of some of the plurality of physical storage resources but not the at least one designated physical storage resource. Moreover, the device may be configured to store data associated with a write operation intended for the at least one designated physical storage resource to the second logical unit. 
     In accordance with an additional embodiment of the present disclosure, a a program of instructions may be embodied in a tangible computer-readable medium. The program of instructions may be operable to, when executed: (a) segment each of a plurality of physical storage resources into a first storage area and a second storage area; (b) activate a first logical unit including each first storage area of the plurality of physical storage resources; (c) place at least one designated physical resource of the plurality of physical storage resources in a powersave mode; (d) activate a second logical unit including the second storage areas of some of the plurality of physical storage resources but not the at least one designated physical storage resources; and (e) store data associated with a write operation intended for the at least one designated physical storage resource to the second logical unit. 
     Other technical advantages will be apparent to those of ordinary skill in the art in view of the following specification, claims, and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
         FIG. 1  illustrates a block diagram of an example system including a redundant storage array having enhanced power management features, in accordance with the present disclosure; 
         FIG. 2  illustrates a flow chart of an example method for managing the power consumption of a redundant storage array having enhanced power management features, in accordance with the present disclosure; and 
         FIG. 3  illustrates a flow chart of an example method for updating a physical storage resource in a storage array having enhanced power management features, in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiments and their advantages are best understood by reference to  FIGS. 1 through 3 , wherein like numbers are used to indicate like and corresponding parts. 
     For the purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, entertainment, or other purposes. For example, an information handling system may be a personal computer, a PDA, a consumer electronic device, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include memory, one or more processing resources such as a central processing unit (CPU) or hardware or software control logic. Additional components or the information handling system may include one or more storage devices, one or more communications ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communication between the various hardware components. 
     For the purposes of this disclosure, computer-readable media may include any instrumentality or aggregation of instrumentalities that may retain data and/or instructions for a period of time. Computer-readable media may include, without limitation, storage media such as a direct access storage device (e.g., a hard disk drive or floppy disk), a sequential access storage device (e.g., a tape disk drive), compact disk, CD-ROM, DVD, random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), and/or flash memory, as well as communications media such wires, optical fibers, microwaves, radio waves, and other electromagnetic and/or optical carriers; and/or any combination of the foregoing. 
     As discussed above, an information handling system may include or may be coupled via a network to an array of physical storage resources. The array of physical storage resources may include a plurality of physical storage resources, and may be operable to perform one or more input and/or output storage operations, and/or may be structured to provide redundancy. In operation, one or more physical storage resources disposed in an array of physical storage resources may appear to an operating system as a single logical storage unit or “logical unit.” 
     In certain embodiments, an array of physical storage resources may be implemented as a Redundant Array of Independent Disks (also referred to as a Redundant Array of Inexpensive Disks or a RAID). RAID implementations may employ a number of techniques to provide for redundancy, including striping, mirroring, and/or parity checking. As known in the art, RAIDs may be implemented according to numerous RAID levels, including without limitation, standard RAID levels (e.g., RAID 0, RAID 1, RAID 3, RAID 4, RAID 5, and RAID 6), nested RAID levels (e.g., RAID 01, RAID 03, RAID 10, RAID 30, RAID 50, RAID 51, RAID 53, RAID 60, RAID 100), non-standard RAID levels, or others. 
       FIG. 1  illustrates a block diagram of an example system  100  including redundant storage array  110  having enhanced power management features, in accordance with the present disclosure. As depicted in  FIG. 1 , system  100  may include a node  102 , a network  108 , a controller  109 , and a storage array  110 . 
     Node  102  may comprise an information handling system and may generally be operable to read data from and/or write data to one of more physical storage resources  112  of storage array  110 . In certain embodiments, node  102  may be a server. In other embodiments, node  102  may be a personal computer (e.g., a desktop or portable computer). As depicted in  FIG. 1 , node  102  may include a processor  103 , a memory  104  communicatively coupled to processor  103 , and a network interface  106  coupled to processor  103 . 
     Processor  103  may comprise any system, device, or apparatus operable to interpret and/or execute program instructions and/or process data, and may include, without limitation a microprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), or any other digital or analog circuitry configured to interpret and/or execute program instructions and/or process data. In some embodiments, processor  103  may interpret and/or execute program instructions and/or process data stored in memory  104  and/or another component of node  102 . 
     Memory  104  may be communicatively coupled to processor  103  and may comprise any system, device, or apparatus operable to retain program instructions or data for a period of time. Memory  104  may comprise random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), a PCMCIA card, flash memory, magnetic storage, opto-magnetic storage, or any suitable selection and/or array of volatile or non-volatile memory that retains data after power to node  102  is turned off. 
     Network interface  106  may be any suitable system, apparatus, or device operable to serve as an interface between node  102  and network  108 . Network interface  106  may enable node  102  to communicate via network  108  using any suitable transmission protocol and/or standard, including without limitation all transmission protocols and/or standards enumerated below with respect to the discussion of network  108 . 
     Although system  100  is depicted as having one node  102 , system  100  may have any number of nodes  102 . 
     Network  108  may be a network and/or fabric configured to communicatively couple node  102  to storage array  110 . In certain embodiments, network  108  may allow node  102  to couple physical storage resources  112  such that the physical storage resources  112  and/or logical units comprising physical storage resources  112  appear to node  102  as locally-attached storage resources. In the same or alternative embodiments, network  108  may include a communication infrastructure, which provides physical connections, and a management layer, which organizes the physical connections between network  108 , network interface  106  and storage array  100 . In the same or alternative embodiments, network  108  may allow block I/O services and/or file access services to physical storage resources  112  disposed in storage array  110 . 
     Network  108  may be implemented as, or may be a part of, a storage area network (SAN), personal area network (PAN), local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), a wireless local area network (WLAN), a virtual private network (VPN), an intranet, the Internet or any other appropriate architecture or system that facilitates the communication of signals, data and/or messages (generally referred to as data). Network  108  may transmit data using any communication protocol, including without limitation, Frame Relay, Asynchronous Transfer Mode (ATM), Internet protocol (IP), other packet-based protocol, small computer system interface (SCSI), advanced technology attachment (ATA), serial ATA (SATA), advanced technology attachment packet interface (ATAPI), serial storage architecture (SSA), integrated drive electronics (IDE), and/or any combination thereof. Further, network  108  may transport data using any storage protocol, including without limitation, Fibre Channel, Internet SCSI (iSCSI), Serial Attached SCSI (SAS), or any other storage transport compatible with SCSI protocol. Network  108  and its various components may be implemented using hardware, software, or any combination thereof. 
     Controller  109  may be any suitable system, device, or apparatus that manages physical storage resources  112  of storage array  110  and/or presents them to node  102  as logical units and/or virtual storage resources (e.g., a RAID controller). For example, if a RAID implemented using the physical storage resources  112  of storage array  110 , controller  109  may control how stored data is mirrored and/or striped among physical storage resources  112 , and may present such RAID as a single logical unit or virtual storage resource to node  102 . In some example embodiments, controller  109  may be an integral part of a storage enclosure housing one or more of physical storage resources  112 . In other example embodiments, controller may be an integral part of node  102 . 
     As depicted in  FIG. 1 , storage array  110  may include one or more physical storage resources  112 , and may be communicatively coupled to node  102  and/or network  108 , in order to facilitate communication of data between node  102  and physical storage resources  112 . Physical storage resources  112  may include hard disk drives, magnetic tape libraries, optical disk drives, magneto-optical disk drives, compact disk drives, compact disk arrays, disk array controllers, and/or any computer-readable medium operable to store data. 
     As shown in  FIG. 1 , each physical storage resource  112  may be segmented into (a) a first storage area referred to herein as an array volume data space  114  and (b) a second storage area referred to herein as a journal space  116 . For example, each physical storage resource  112  may be partitioned to create array volume data space  114  and journal space  116 . As shown in  FIG. 1 , and as described in greater detail below with respect to  FIGS. 2 and 3 , a data space logical unit  118  may be activated to include one or more array volume data spaces  114 . In certain embodiments, data space logical unit  118  may appear to an operating system executing on node  102  as a single logical storage unit or virtual resource. Thus, node  102  may “see” data space logical unit  118  instead of seeing each individual physical storage resource  112 . In such embodiments, data to be written to and/or read from storage array  110  may be respectively written to and/or read from data space logical unit  118 . 
     Also, as shown in  FIG. 1 , and as described in greater detail below with respect to  FIGS. 2 and 3 , a journal space logical unit  120  may include journal spaces  116  of some but not all (e.g., all but one) of physical storage resources  112 . However, unlike data space logical unit  118 , journal space logical unit  120  may not be presented to or “seen” by node  102  as a logical unit in certain embodiments of this disclosure. Instead, information and/or data associated with one or more physical storage resources  112  in a powersave mode may be written to and/or read from journal space logical unit  120  by controller  109 , as described in greater detail below with respect to  FIGS. 2 and 3 . 
     Although the embodiment shown in  FIG. 1  depicts storage array  110  having five physical storage resources  112 , storage array  210  may have any number of physical storage resources  112 . In certain embodiments, system  100  may include a storage enclosure to hold and power controller  109  and/or one or more physical storage resources  112 . 
     Although  FIG. 1  depicts that node  102  is communicatively coupled to storage array  110  via network  108 , node  102  may be communicatively coupled to one or more physical storage resources  112  without the need of network  108  or another similar network. For example, in certain embodiments, one or more physical storage resources  112  may be directly coupled and/or locally attached to one or more nodes  102 . 
       FIG. 2  illustrates a flow chart of an example method  200  for managing the power consumption of redundant storage array  110 , in accordance with the present disclosure. According to one embodiment, method  200  preferably begins at step  202 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of system  100 . As such, the preferred initialization point for method  200  and the order of the steps  202 - 212  comprising method  200  may depend on the implementation chosen. 
     At step  202 , node  102 , controller  109 , and/or another suitable component of system  100  may segment each physical storage resource  112  into an array volume data space  114  and a journal space  116 . For example, each physical resource  112  may be segmented by creating separate partitions for each of its respective array volume data space  114  and journal space  116 . In certain embodiments, the journal space  116  may be implemented using inner disk tracks of each of physical storage resource  112 . The relative sizes of each array volume data space  114  and journal space  116  may be selected in any suitable manner. For example, the relative sizes may be pre-determined by a manufacturer, a network administrator, information technology technician, and/or another user. In some embodiments, each array volume data space  114  may be of approximately identical size. The same or alternative embodiments, each journal space  116  may be of approximately identical size. 
     At step  204 , controller  109  may activate data space logical unit  118  including array volume data spaces  114 . Data space logical unit  118  may be a redundant storage array, and may be implemented using any suitable RAID level. Once activated, data space logical unit  118  may be presented to or “seen” by node  102  as a single logical unit. Accordingly, data to be written and/or read by node  102  by be written and/or read to data space logical unit  118 . 
     At step  206 , node  102 , controller  109 , and/or another suitable component of system  100  may identify one or more physical storage resources  112  to be placed in a powersave mode. The physical storage resource(s)  112  to be placed in the powersave mode may be identified in any suitable manner. For example, the physical storage resources(s)  112  to be placed in a powersave mode may be identified according to an established policy and/or algorithm (e.g., based on a program and/or logic resident on node  102  and/or controller  109 ) that determines when to place one or more physical storage resource(s)  112  in powersave mode. 
     At step  208 , node  102 , controller  109 , and/or another suitable component of system  100  may activate journal space logical unit  120  including those journal spaces  116   b - e  of physical storage resources  112   b - e  other than the identified physical storage resource(s)  112  (e.g., physical storage resource  112   a ). Journal space logical unit  120  may be a redundant storage array, and may be implemented using any suitable RAID level. In certain embodiments, journal space logical unit  120  may employ a RAID level different than that of data space logical unit  118 . For example, data space logical unit  118  may employ RAID 5, while journal space logical unit  120  employs RAID 10. In certain embodiments, journal space logical unit  120  may not be presented to or “seen” by node  102  as a logical unit. Instead, journal space logical unit  120  may be used to journal or catalog write operations intended for physical storage resource  112   a  while physical storage  112   a  is in powersave mode, as described in further detail below. 
     At step  210 , node  102 , controller  109 , and/or another suitable component of system  100  may place the identified physical storage resource(s)  112  in a powersave mode. A powersave mode may include any mode and/or state of a physical storage resource  112  in which it may consume less power than if it were operating in a normal mode. For example, placing a physical storage resource  112  in a powersave mode may include spinning it down, placing it in a lower power “standby” or “sleep” state, or removing power from it entirely. For clarity, the remaining discussion of  FIG. 2  and  FIG. 3  assumes that physical storage resource  112   a  is the identified physical storage resource that is placed in a powersave mode. However, it is understood that any combination of physical storage resources  112   a - 112   e  may be placed in a powersave mode at steps  206 - 210  in accordance with this disclosure. 
     At step  212 , controller  109  and/or another suitable component of system  100  may store all writes intended for the powered-down physical storage node  112   a  to the journal space logical unit  120 . In certain embodiments, writes to journal space logical unit  120  may include a “journaled” write, wherein information regarding the destination of a write may also be written in addition to the data to be written. For example, writes to journal space logical unit  120  may include information regarding the destination sector, track, and/or block of the powered-down physical storage node  112   a  corresponding to data written to journal space logical unit  120 . In addition, writes to journal space logical unit  120  may include information regarding the destination physical storage node  112  corresponding to data written to journal space logical unit  120  (e.g., in embodiments where more than one physical storage node  112  is placed in powersave mode). 
     In the event node  102  issues a read operation to data space logical unit  118  for data stored in powered-down physical storage resource  112   a , in certain embodiments controller  109  may maintain physical storage resource  112   a  in powersave mode and determine the data to be communicated to node  102  in response to the read operation based on data stored on the remaining physical storage nodes  112   b - e . For example, when a read operation is made for a particular block of physical storage resource  112   a , controller  109  may first read journal space logical unit  120  to determine whether the particular block was the destination of a write that occurred after physical storage resource  112   a  was placed in powersave mode. If the particular block was the destination of such a write, controller  109  may respond to the read operation with the relevant data stored in journal space logical unit  120 . On the other hand, if such a write has not occurred after physical storage resource  112   a  was placed in powersave mode, any data that existed on array volume data space  114   a  of physical storage resource  112   a  prior to entering power-save mode may be determined based on data present on array volume data spaces  114   b - e , because of the redundant nature of data space logical unit  118 . Accordingly, in such a scenario, controller  109  may respond to the read operation by performing a parity operation or other suitable operation with respect to the relevant data stored in array volume data spaces  114   b - e.    
     Although  FIG. 2  discloses a particular number of steps to be taken with respect to method  200 , it is understood that method  200  may be executed with greater or fewer steps than those depicted in  FIG. 2 . In addition, although  FIG. 2  discloses a certain order of steps to be taken with respect to method  200 , the steps comprising method  200  may be completed in any suitable order. Method  200  may be implemented using system  100  or any other system operable to implement method  200 . In certain embodiments, method  200  may be implemented partially or fully in software embodied in tangible computer-readable media. 
       FIG. 3  illustrates a flow chart of an example method  300  for updating a physical storage resource  112  from a powersave mode, in accordance with the present disclosure. According to one embodiment, method  300  preferably begins at step  302 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of system  100 . As such, the preferred initialization point for method  300  and the order of the steps  302 - 312  comprising method  300  may depend on the implementation chosen. 
     At step  302 , node  102 , controller  109 , and/or another suitable component of system  100  may determine that one or more of the powered-down physical storage resources  112  (e.g., physical storage resource  112   a  in the example discussed with respect to method  200 ) is to exit powersave mode. For example, a determination to exit a powersave mode may be made based on a policy and/or algorithm that defines when a physical storage resource  112  is to be placed in or removed from powersave mode. In some embodiments, such a policy and/or algorithm may establish a time schedule for placing one or more of physical storage resources  112  in a powersave mode and/or removing them from the powersave mode. In addition or alternatively, a policy and/or algorithm may dictate that a physical storage resource  112  is to be removed from powersave mode when data and information relating to the particular physical storage resource  112  and stored in journal space logical unit  120  has reached a threshold (e.g., a certain percentage of the available storage space of journal space logical unit  120 ). As a further example, a physical storage resource  112  may be removed from power save mode in the event of a failure of another physical storage resource  112  in the storage array  110 . 
     At step  304 , in response to a determination that physical storage resource  112   a  is to exit powersave mode, controller  109  may remove physical storage resource  112   a  from powersave mode (e.g., by returning power to it or issuing a command or message to exit a standby or sleep state). 
     At step  306 , controller  109  and/or another suitable component of system  100  may update the powered-up physical storage resource  112   a  based on information and/or data stored in journal space logical unit  120 . For example, physical storage resource  112   a  may be updated based on journaled writes made to journal space logical unit  120  which include the write data along with destination information associated with the write data. At step  308 , controller  109  and/or another suitable component of system  100  may deactivate journal space logical unit  120  after updating physical storage resource  112   a.    
     At step  310 , controller  109  and/or another component of system  100  may determine whether the powersave mode was exited because of a failure of a physical storage resource  112 . If the powersave mode was not exited because of a failure of a physical storage resource  112 , method  300  may end. However, if the powersave mode was exited because of a failure of a physical storage resource  112 , data space logical unit  118  may be in a degraded state and the failed physical drive may need to be replaced and rebuilt. In such a case, method  310  may proceed to step  312 . 
     At step  312 , controller  109  and/or another suitable component of system  100  may rebuild array volume space  114  of failed physical storage resource  112  from array volume data spaces  114  of the remaining physical storage resources  112 , using any suitable data rebuild process. 
     Although  FIG. 3  discloses a particular number of steps to be taken with respect to method  300 , it is understood that method  300  may be executed with greater or fewer steps than those depicted in  FIG. 3 . In addition, although  FIG. 3  discloses a certain order of steps to be taken with respect to method  300 , the steps comprising method  300  may be completed in any suitable order. Method  300  may be implemented using system  100  or any other system operable to implement method  300 . In certain embodiments, method  300  may be implemented partially or fully in software embodied in tangible computer-readable media. 
     Although the methods set forth above discuss a specific example whereby physical storage resource  112   a  is placed in a powersave mode, any combination of one or more physical storage resources  112  may be placed in a powersave mode in accordance with the systems and methods disclosed. For illustrative purposes only, a specific example of an embodiment wherein more than one physical storage resource  112  may be placed in a powersave mode in one in which storage array  110  includes a four-physical storage resource RAID 10 (assume for purposes of this example that physical storage resource  112   e  is not present). In this example, storage resources  112   a - b  may be placed in a powersave mode while journal spaces  116   c - d  comprises the journal space logical unit  120 . The journal space logical unit  120  in this embodiment may be a RAID 1. 
     In addition, in accordance with certain embodiments of the present invention, various physical storage resources  112  in storage array may be placed in and removed from a powersave mode according to a scheduling policy or algorithm. For example, a manufacturer, network administrator, information technology technician, or another user may establish a schedule whereby physical storage resources  112  “take turns” being placed in powersave mode. As a specific example, a network administrator may establish a policy whereby storage resource  112   a  is placed in powersave mode on Monday, storage resource  112   b  is placed in powersave mode on Tuesday, storage resource  112   c  is placed in powersave mode on Wednesday, storage resource  112   d  is placed in powersave mode on Thursday, storage resource  112   e  is placed in powersave mode on Friday, and no storage resources are placed in powersave mode on Saturday and Sunday. Under this scenario, storage resource  112   a  would be placed in powersave mode on Monday in accordance with a method similar to method  200 . On Tuesday, storage resource  112   a  would be removed from powersave mode in accordance with a method similar to method  300 , and storage resource  112   b  would be placed in powersave mode on Monday in accordance with a method similar to method  200 , and so on. As another specific example, in an embodiment whereby storage array  110  includes a four-physical storage resource RAID 10 (e.g., without physical storage resource  112   e ), physical storage resources  112   a - 112   b  may be placed in powersave mode on odd-numbered days, and physical storage resources  112   c - 112   d  may be placed in powersave mode on even-numbered days. 
     Using the methods and systems disclosed herein, problems associated conventional approaches to management of power consumption in a storage array may be reduced or eliminated. For example, because the methods and systems disclosed may allow for reduced power consumption in redundant storage arrays by placing one or more physical storage resources in a powersave mode while maintaining the capability to recover from a single physical storage resource failure without data loss. 
     In addition, the power savings achieved in certain embodiments may significantly outweigh the associated loss of storage capacity required. For example, in a five-physical storage resource RAID 5 logical unit, a user may desire to implement a journal space logical unit that can redundantly store 10% of the capacity of the physical storage resource  112  to be powered down. Such an implementation would require each journal space  116  to use approximately 3⅓% of the storage space of its associated physical storage resource  112  (e.g., if physical storage resource  112   a  is to be placed in powersave, each of journal spaces  116  would need to be 3⅓% of the storage space of a physical storage resource  112  in order to store 10% of the capacity of physical storage resource  112   a  while also maintaining redundancy). Thus, in this particular example, a 20% power consumption reduction may be achieved while sacrificing only 3⅓% in storage capacity. 
     Another potential advantage of certain embodiments disclosed herein is that by reducing the amount of time each physical storage resource  112  in a storage array is fully powered, the mean time before failure (MTBF) of each individual physical storage resource may increase, particularly in embodiments were physical storage resources  112  are placed in powersave mode in a round-robin fashion. Any increase of MTBF for individual physical storage resources  112  may not only decrease the occurrence of physical storage resource failures necessitating the rebuilds thereof, but may also increase the MTBF for the redundant storage array  110  itself, thus providing increased data integrity. 
     Although the present disclosure has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and the scope of the invention as defined by the appended claims.