Abstract:
To prevent current inrush from exceeding power limitations of a power supply or a power domain in a multiple disk drive system the drives are powered-on in a controlled sequence. In a multi-drive blade storage subsystem, a subsystem control module inventories the locations of the hard drives in one or more drive enclosure blades and maintains information about the boundaries of one or more power domains. The subsystem control module may direct one of several drive power-on sequences, none of which allow current inrush to exceed the allowable current of each power domain.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to storage subsystems and, in particular, to managing the power-on of hard disk drives in such a subsystem 
       BACKGROUND ART 
       [0002]    Storage subsystem enclosures housing multiple hard disk drives (HDDs) typically have power supplies which are designed to handle the full current required when power to the enclosure, and therefore to the HDDs, is turned on, even though the momentary inrush current drawn by the HDDs when turned on may be more than twice their normal operating current. For redundancy, a pair of power supply units (PSUs) may be provided. Larger storage subsystem enclosures may include more than one pair of redundant PSUs, with each pair supplying power to a portion of the HDDs, each portion defining a power “domain”. However, the power demands of each domain are still within the capability of a power supply, even during the power-on process. 
         [0003]    Blade computing is a relatively recent and fast growing innovation. Various components, such as processors, servers, storage, network switches, power supplies, cooling, etc., are provided on cards (known as “blades”) which plug into a back- or mid-plane slot in a chassis. Blade computing, being self contained and with fewer cables, increases processing density in a more compact and less expensive package than traditional computer systems, such as server farms. In a standard power control procedure, a central management module provides a power-on command to each blade. Such a procedure has been adequate for single blades and double-wide blades (those taking two slots). 
         [0004]    An even more recent product, the BladeCenter® from IBM®, incorporates a serial attached SCSI (SAS) storage subsystem in a blade housing. The BladeCenter chassis includes two power domains, each sourced by a redundant pair of power supply units. Each domain provides power to one-half of the installed blades. The SAS storage subsystem includes a pair of RAID controller blades and up to four triple-wide drive enclosure blades. Up to 24 HDDs may be installed in each drive enclosure blade. Although the power requirements for each drive enclosure blade is designed to be within the power requirements of three single blades, when an HOD first spins up, it may draw more than double its maximum operating current. Powering up all HDDs in a BladeCenter would far exceed the power envelope and perturbate the power domain. Consequently, a new power management system is desirable for systems and subsystems such as the BladeCenter storage subsystem. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides systems and methods to prevent current inrush from exceeding power limitations of a power supply or a power domain in a multiple disk drive system by powering-on the drives in a controlled sequence. In a multi-drive blade storage subsystems a subsystem control module inventories the locations of the hard drives in one or more drive enclosure blades and maintains information about the boundaries of one or more power domains. The subsystem control module may direct one of several drive power-on sequences, none of which allow current inrush to exceed the allowable current of each power domain. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1A and 1B  are front and rear perspective views, respectively, of a blade chassis in which the present invention may be implemented; 
           [0007]      FIG. 2  is a perspective view of a disk enclosure blade which may be inserted into the chassis of  FIGS. 1A and 1B ; 
           [0008]      FIG. 3  is a cut-away view of a multi-drive tray which may be inserted into the disk enclosure blade of  FIG. 2 ; 
           [0009]      FIG. 4  schematically illustrates power domains in a blade storage subsystem; 
           [0010]      FIG. 5  is a more detailed block diagram of the power domains of  FIG. 4  within a blade storage subsystem; 
           [0011]      FIG. 6  illustrates the power distribution within one drive enclosure blade; and 
           [0012]      FIG. 7  is a block diagram of a blade storage subsystem in which the present invention may be implemented. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]      FIGS. 1A and 1B  are front and rear perspective views, respectively, of a blade chassis  100  in which the present invention may be implemented. The chassis  100  includes a housing  102  a mid- or back-plane  104  and slots  106  into which blades, such as a drive enclosure blade (DEB)  200 , are inserted from the front ( FIG. 1A ) to mate with appropriate connectors on the front of the mid-plane  104 . The IBM eServer# BladeCenter chassis includes fourteen such slots in accessible from the front. The rear of the chassis  100  ( FIG. 1B ) is configured to hold additional components or modules. Such modules may include, for example, two blowers  108 A,  108 B, up to two redundant pairs of power supply units (PSUs)  110 A,  110 B,  112 A,  112 B, a redundant pair of serial attached SCSI (SAS) switches  114 A,  114 B, and a management module  116 . Such components are inserted from the rear of the chassis  100  to mate with appropriate connectors on the rear of the mid-plane  104 . 
         [0014]      FIG. 2  is a perspective view of a DEB  200  which may be inserted into the chassis  100 . Each DEB  200  fits into three contiguous slots  106  in the chassis  100  and up to four DEBs  200  may be installed in the chassis  100 . In addition, a redundant pair of RAID controller blades (RCBs)  118 A,  118 B may be installed in the chassis  100 . Up to eight multi-drive trays  300  may be inserted into slots in the DEB  200  along with a redundant pair of local drive controller cards  202 A,  2028 . The multi-drive trays  300  and controller cards  202 A,  202 B mate with appropriate connectors on a back-plane  204  within the DEB  200 . As illustrated in the cut-away view of  FIG. 3 , a multi-drive tray  300  may house up to three hard disk drives (HDDs)  302 A,  302 B,  302 C. Thus, each DEB  200  may house up to twenty-four HDDs and a full chassis  100  may house up to ninety-six HDDs. 
         [0015]      FIG. 4  schematically illustrates subsystem power domains in the blade storage subsystem. A first pair of redundant power supply units, PSU 1   110 A and PSU 2   110 B, comprise a first subsystem power domain  402  supplying power to slots  1 - 7  in the chassis  100 . A second pair of redundant power supply units, PSU 3   112 A and PSU 4   1128  comprise a second subsystem power domain  404  supplying power to slots  8 - 14 . If one of the PSUs in a domain fails, service will be continued by the other PSU, thereby ensuring uninterrupted operation. In the illustrated configuration, DEB 1  and DEB 2   200 A,  200 B, are wholly within the first subsystem power domain  402  and DEB 4   200 D and the two RCBs  116 A,  116 B are wholly within the second subsystem power domain  404 . DEB 3   200 C, in slots  7 - 9 , spans both subsystem power domains  402 ,  404 . 
         [0016]      FIG. 5  is a more detailed block diagram of the subsystem power domains  402 ,  404 . As previously described each PSU  110 A,  110 B,  112 A,  112 B connects to the rear of the mid-plane  104  while the DEBs  200 A- 200 D connect to the front of the mid-plane  104 . The mid-plane  104  includes two pairs of parallel power buses, one pair for each subsystem power domain  402 ,  404 . PSU 1   110 A is coupled to a first power bus  500 A and PSU 2   110 B is coupled to a second power bus  500 B and PSU 3   112 A is coupled to a third power bus  502 A and PSU 4   112 B is coupled to a fourth power bus  502 B. In the front slots  106 , each DEB  200  includes four power connectors with which to couple to the mid-plane  104 . In DEB 1   200 A, the first two power connectors  1 A,  1 B are coupled to PSU 1   110 A and PSU 2   110 B, respectively and are part of a first local power domain (within the DES). Similarly, the last two power connectors  3 A,  3 B are coupled to PSU 1   110 A and PSU 2   110 B, respectively, and are part of a second local power domain. The middle two power connectors  2 A,  28  are not used. DEB 2   200 B is coupled to the first and second power buses  500 A,  500 B in the same manner, In DEB 4   200 D, the first two power connectors  10 A,  10 B are coupled to PSU 3   112 A and PSU 4   1128 , respectively, and are part of a first local power domain. Similarly, the last two power connectors  12 A,  128  are coupled to PSU 3   112 A and PSU 4   112 B, respectively, and are part of a second local power domain. DEB 3   200 C spans the two subsystem power domains  402 ,  404 ; the first two power connectors  7 A,  7 B are coupled to PSU 1   110 A and PSU 2   110 B, respectively, and are part of a first local power domain while the last two power connectors  9 A,  9 B are coupled to PSU 3   112 A and PSU 4   112 B, respectively, and are part of a second local power domain. The two RCBs  118 A,  118 B in chassis slots  13  and  14  are within the second subsystem power domain  404  and are each coupled to power buses  502 A,  502 B. RCB 1   118 A is coupled through power connectors  13 A and  138  and RCB 2   118 B is coupled through power connectors  14 A and  148 . It will be appreciated that the illustrated configuration is only one example and that the present invention contemplates other configurations. 
         [0017]      FIG. 6  illustrates the power distribution within one DEB, such as DEB 1   200 A. Four of the multi-drive trays  300 A- 300 D and one local drive controller card  202 A are within a first local power domain  600 A and the other four multi-drive trays  300 E- 300 H and the other local drive controller card  202 B are within a second local power domain  600 B. Although both local power domains  600 A,  600 B in DEB 1   200 A are part of the first subsystem power domain  402 , in DEB 3   200 C, the first local power domain  600 A would be part of the first subsystem power domain  402  and the second local power domain  600 B would be part of the second subsystem power domain  404 . 
         [0018]      FIG. 7  is a block diagram of a blade storage subsystem in which the present invention may be implemented. In addition to the previously described components, the blade storage subsystem includes redundant subsystem SCSI enclosure services (SES) modules  700 A,  700 B (collectively referred to hereinafter as subsystem SES module  700 ) within the two SAS switches  114 A,  114 B and a local SES module  710 A,  710 B within each local drive controller card  202 A,  202 B, respectively (and collectively referred to hereinafter as local SES module  702 ). The subsystem SES modules  700 A,  700 B and the local SES modules  710 A,  710 B include logic for managing the power-on of multiple HDDs in the storage subsystem. 
         [0019]    In operation, when the subsystem is powered on, such as with a power switch on the chassis  100 , the management module  116  transfers control of the power-on sequence to the subsystem SES module  700 . The subsystem SES module  700  performs a discovery operation to determine how many HDDs are installed and where each is located. The location includes the location of the multi-tray module in which each HDD is installed and the location of the DEB in which the multi-tray module is installed. The location also includes the power domain in which each HDD is located. The location information is captured in a table  702  or other comparable data structure within the subsystem SES  700 . Such a table may be generated the first time the subsystem is powered on and updated each time a module is inserted or removed from the chassis  100 . Alternatively, the table may be generated during each power-on sequence. During the discovery operation, each local SES  710  reports the mapping of SAS port addresses to physical addresses within its DEB. The subsystem SES  700  then compiles the mapping information from the local SES modules  710  into the table  702  along with information about power domain boundaries. 
         [0020]    The subsystem SES  700  then directs the local SES modules  710  to commence powering on the HDDs in such a way that the inrush current does not exceed the limits of any power domain. In one such sequence, the subsystem SES  700  directs specific DEBs to power-on specific HDDs in a predefined order, again established such that the inrush current does not exceed the limits of any power domain. This procedure may be particularly beneficial when a DES spans two power domains. In an alternate sequence, the subsystem SES  700  directs one local SES module  710  in each power domain to power-on the HDDs in the respective DEBs. When those two local SES modules  710  report back that the HDDs are powered on, the subsystem SES  700  directs another local SES module  710  in each power domain to power-on the HDDs in the respective DEBs. The process continues until all HDDs are powered on. In a variation of the latter process, depending upon the power domain configuration and current limitations, the subsystem SES  700  may direct more than one local SES module  710  in each power domain to power-on the HDDs. For example, in a two domain system illustrated in the Figs., powering-on the HDDs in two DEBs at the same time in the same power domain may exceed the power limits of a domain. However, the subsystem SES  700  may instead direct DEB 1  and DEB 4   200 A,  200 D, in power domains  1  and  2   402 ,  404 , and DEB 3   200 C, spanning the two power domains  402 ,  404 , to power-on the respective HDDs. 
         [0021]    In addition, each local SES module  710  may power-on fewer than all of the HDDs at a time in a DEB  200  if powering on all would exceed the power limits of the domain. In an alternative sequence powering-on of DEBs may be partially overlapped to speed the entire process. Once the initial power spike of one DEB has dissipated, the next DEB may be powered-on with little risk of exceeding power restrictions. 
         [0022]    The present invention also accommodates the process of hot-plugging one or more DEBs or drive trays. It will be appreciated that hot-plugging a module can generate the same power surge that a convention power-on can generate. Consequently, in response to a signal that one or more DEBs or drive trays have been hot-plugged, the subsystem SES module  700  directs the appropriate local SES module  710  to power on the new DEBs or drives in such a manner that the power limits are not exceeded. 
         [0023]    It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media such as a floppy disk, a hard disk drive, a RAM, and COD-ROMs and transmission-type media such as digital and analog communication links. 
         [0024]    The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. It will be appreciated that the present invention is not limited to use with a subsystem of the foregoing description. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. Moreover, although described above with respect to methods and systems, the need in the art may also be met with a computer program product containing instructions for managing the power-on of multiple hard disk drives in a storage subsystem.