Abstract:
Systems and methods for replicating data from a first site to a second site remote from said first site are described. An embodiment includes storing compressed data on a hard disk appliance, reading said data without decompressing said data, sending said data over a wide-area-network (WAN) in a compressed state, and storing said data on a second hard disk appliance remote from said first hard disk appliance in its compressed state without performing an additional compression operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application No. 60/654,714, filed on Feb. 17, 2005. This application is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to systems and methods for storing electronic data and has applicability to enterprise data backup systems. 
     2. Description of the Related Art 
     Improving backup and restore performance is a continuing desire of enterprise data managers. In a typical computing environment, magnetic disk drives are used as the primary storage mechanism for active data, whereas magnetic tapes are used for data backup and archive. The magnetic disks provide rapid and reliable access to data, but they are perceived as being more expensive. In addition, since they are non-removable, they are at risk of physical disasters. Magnetic tape storage is perceived as being less expensive and, because tape cartridges are removable, they can be moved to offsite locations to protect against physical disasters. Therefore, most backup software in use has been optimized for use with magnetic tape technology. 
     Reading and writing data on a tape requires that the reel be unwound until the desired location is found. Once in the appropriate location, the read or write operation can begin. Because of the mechanical nature of this access, read and write operations are slow and often fail. In many situations, it would be beneficial to provide the random access speed and the reliability of a magnetic disk drive to backup systems while still allowing for the possibility of offsite storage. As a result, a new category of magnetic disk systems is becoming popular called virtual tape technology. 
     Virtual tape systems are magnetic disk systems that transparently emulate a tape drive and/or a tape library. They provide the same physical connections to a host, such as SCSI, Fibre Channel or Ethernet. This allows them to connect in the same way as the tape systems they are replacing or augmenting. They also provide the same logical response to tape drive and robot commands, which allows the same backup software to remain in use. The emulator is also able to send the host computer the expected tape-drive interrupt signals such as beginning-of-tape, end-of-tape, and inter-record-gap. In this case, such a system can plug right in to an existing tape based storage system without a need for the user to change the storage network or software environment. 
     Although such systems have been successful in the marketplace, the currently available devices still do not fully take advantage of the properties of disk storage in a way that provides maximum flexibility and usefulness. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a method of replicating data from a first site to a second site remote from the first site is provided. The method comprises storing compressed data on a hard disk appliance, and reading the data without decompressing the data. The data is sent over a wide-area-network (WAN) in a compressed state, and stored on a second hard disk appliance remote from the first hard disk appliance in its compressed state without performing an additional compression operation. 
     In other embodiments, the invention comprises methods of managing data storage. In one embodiment, such a method includes backing up data on a first hard disk storage appliance that is configured to emulate a tape based storage appliance, and replicating the data on a second hard disk storage device remote from the first hard disk storage device in response to an unload command sent to the first hard disk storage device. In another embodiment, a method of managing data storage comprises backing up data on a first hard disk storage appliance that is configured to emulate a tape based storage appliance, and replicating the data on a second hard disk storage device remote from the first hard disk storage device in response to completion of a scheduled backup operation. In another embodiment, a method of managing data storage comprises backing up data on a first hard disk storage appliance that is configured to emulate a tape based storage appliance, and replicating the data on a second hard disk storage device remote from the first hard disk storage device during the process of backing up the data on the first hard disk storage device. In another embodiment, a method of managing data storage comprises backing up data on a first hard disk storage appliance that is configured to emulate a tape based storage appliance according to a first user defined periodic schedule; replicating the data on a second hard disk storage device remote from the first hard disk storage device according to a second user defined periodic schedule. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of one embodiment of a data backup system. 
         FIG. 2  is a diagram of a multi-site replication system 
         FIG. 3  is a block diagram of the operation of one embodiment of the system of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Preferred embodiments of the present invention will now be described with reference to the accompanying Figures, wherein like numerals refer to like elements throughout. The terminology used in the description presented herein is intended to be interpreted in its broadest reasonable manner, even though it is being utilized in conjunction with a detailed description of certain specific preferred embodiments of the present invention. This is further emphasized below with respect to some particular terms used herein. Any terminology intended to be interpreted by the reader in any restricted manner will be overtly and specifically defined as such in this specification. 
       FIG. 1  illustrates one example of a system including a hard disk based appliance with tape emulation features that can be used in a data protection environment. In this system, application servers  12  are connected to each other and to a backup server  16  over a network  14 . The backup server  16  communicates with the disk appliance  18  and to the tape system  20 . In some embodiments, the backup server communicates directly with the disk appliance  18 , and the tape system is controlled by the disk appliance directly, rather than by the backup server  16 . Additional features of such embodiments are described in U.S. application Ser. No. 11/356,726, filed on even date herewith, entitled Tape Library Emulation with Automatic Configuration and Data Retention, which application is hereby incorporated by reference in its entirety. It will be appreciated that multiple disk appliances and tape systems may be connected in the storage area network. 
     Backups from application servers  12  are received by appliance  18  (via the backup server  16 ) and are written to disk based (preferably RAID) storage of appliance  18 . The disk appliance  18  may include an internal disk drive array, and may alternatively or additionally connect to an external disk drive array through a storage adapter which may, for example, be configured as a Fibre Channel or SCSI interface. 
     Appliance  18  and/or backup server  16  may then automate the process of transferring the data stored on disk media to physical tape media in tape system  20  for archival purposes. The transfer of the disk stored data to physical tape media may be done without user intervention on a periodic basis. 
     It will be appreciated that the hardware components, functionality, and software present in the backup server  16 , disk appliance  18 , and tape drive/library can be combined and/or separated in various ways. For example, the disks of appliance  18  can be located in a separate device. As another example, the tape drive/library  20  hardware and functions can be integral with the disk appliance  18  rather than provided as a separate unit. As described above, the appliance  18  can be configured to interact with the backup server  16  in exactly the same manner and format of communication as the tape drive/library  20 . In this way, software on the backup server  16  that is configured to communicate and store data using tape commands and tape data formats can utilize the disk based appliance  18  without modification. Speed is still improved in many cases such as restore operations, however, because tape commands such as moving to a desired block can be accomplished on disk with the virtual tape much faster than a physical tape cartridge in a physical tape drive. 
     Typically, for enterprises utilizing data backup hardware and procedures as described in  FIG. 1 , each location of the enterprise would have a system as illustrated in  FIG. 1  which would be separately operated and managed so as to backup and archive data for each separate location. Tapes were typically physically moved offsite from each location to a central facility. This results in inefficiency and expense.  FIGS. 2 and 3  illustrate a multi-site replication architecture in accordance with some embodiments of the invention that avoids many of the problems encountered in enterprises having multiple separate locations with data backup requirements. In this embodiment, both a central location  26  and a satellite location  28  include most or all of the system components as outlined above with regard to  FIG. 1 . 
     In the embodiment of  FIG. 2 , the two locations  26 ,  28  are in communication over a wide area network (WAN)  30  which may include the Internet, for example. In some advantageous embodiments, several satellite locations are coupled through the WAN to a common central location. The facilities  26 ,  28  are remote from one anther, where remote means that they are coupled through a WAN. They will typically also be geographically remote. As illustrated in  FIG. 2 , in this architecture, it is not necessary for the satellite location  28  to have an onsite tape storage system  20 . Rather, data files that are backed up onto appliance  18  are transferred over the WAN  30  for archiving onto physical tapes by the tape storage system  20  at the central location  26 . In some advantageous embodiments, files are moved from the satellite location  28  to the central location  26  in replication processes that transfer images of virtual tapes on disk appliance  18 B to virtual tapes on disk appliance  18 A. Replication processes are illustrated in more detail in  FIG. 3 . 
     Referring now to  FIG. 3 , the replication process is managed by a replication server  32  typically running at the central location  26 . After receiving a replication request, the replication server spawns a data mover thread  34  that runs to completion. The replication request can come from a management interface  36  accessible to system users. The management interface can be used to issue immediate replication requests, or can be used to schedule timed or periodic replication requests that are managed by a scheduling utility  38  such as the Linux cron daemon. In this way, data backups to disk appliance  18 B can be performed on a first periodic schedule defined with the backup server software, and replication processes can be performed on a second different schedule defined by the replication server if desired. Replication can also be performed in conjunction with backup processes as described below. 
     The data mover performs block reads from the source target  40  and block writes to the destination target  42  during a replication process. In some advantageous embodiments, the source tape and drive and the destination tape and drive are virtual tape system devices implemented in the disk based appliances  18 B and  18 A. 
     There are four primary ways in which a user may replicate a tape. Scheduled replication allows the user to specify a time in which regular copies are made of a Source Target. In this process the user identifies a Source Target for replication and a Destination Target. If the Destination Target is a Media Changer device, the user will identify which volume to use as the backup medium. The user will set the schedule parameters. This may include time, day-of-week and/or daily. Immediate replication is performed similarly, but a replication request command is sent to the replication server immediately instead at a future scheduled time. 
     Post-Backup Replication is provided by using a small utility that will send an in-band request to the backed-up tape device. The request may consist of a vendor-specific write Command Descriptor Block (CDB). The data portion of this write may contain a buffer with the replication parameters in key/value form. Upon identifying an in-band replication request, the Target Driver will parse the message and send a Replication Request Message to the Replication Server. 
     Auto-Replication on Unload is another example of Post-Backup replication. In this case, during initial replication setup, a choice under the schedule parameters may include a “Replication on Unload” option. When the target driver detects an “Unload,” a replication request message is sent via the normal In-Band mechanism. The replication server will determine if the unloaded source target is scheduled for a “Replicate on Unload.” If it is, then normal replication processing is started. 
     Because data transfer over the WAN is typically slow compared to local network transfers, sending and receiving compressed data will greatly reduce the amount of data transferred over a potentially slow link. To implement this, if the data on the source tape is already compressed, a special Read CDB operation code can be used to read the data without decompressing it. If the data on the source tape is uncompressed, it can be compressed after a regular Read operation and before transmitting to the destination tape. 
     Furthermore, a special Write CDB operation code can be used for writes to the destination tape. The special write basically instructs the driver to write the data as compressed without first compressing it. 
     This approach can thus be implemented with two vendor-specific CDBs, one for Reads and one for Writes. An alternative approach could use a vendor-specific Mode Page. 
     An example Read Compressed CDB can be constructed to follow the standard SCC Read: 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
               
               
             
               
               
             
           
               
                   
               
             
             
               
                 Byte/Bit 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
               
               
                   
               
             
          
           
               
                 0 
                 Operation Code (0xC1) 
               
             
          
           
               
                 1 
                 Logical Unit Number 
                 Reserved 
                 SILI 
                 Fixed 
               
             
          
           
               
                 2 
                 (MSB) 
               
               
                 3 
                 Transfer Length 
               
               
                 4 
                 (LSB) 
               
               
                 5 
                 Control 
               
               
                   
               
             
          
           
               
                 SILI: 
                 0 = report incorrect block length when it occurs 
               
               
                   
                 1 = do not report incorrect block length 
               
               
                 Fixed: 
                 0 = return one variable length block with length in bytes 
               
               
                   
                 specified by the Transfer Length 
               
               
                   
                 1 = return the number of fixed length blocks specified by 
               
               
                   
                 by the Transfer Length; Block length is specified in the 
               
               
                   
                 the Mode Select command. 
               
             
          
         
       
     
     If the data is uncompressed, a check condition is returned with a special code in the sense data. When the data is returned uncompressed, it is compressed before transmission to the Destination Target. An alternative approach is to have the READ COMPRESSED call always return compressed data. If it is uncompressed, the driver will compress it before returning it. 
     An example Write Compressed CDB can be constructed to follow the standard SCC Write: 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
             
               
               
             
           
               
                   
               
             
             
               
                 Byte/Bit 
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
               
               
                   
               
             
          
           
               
                 0 
                 Operation Code (0xC2) 
               
             
          
           
               
                 1 
                 Logical Unit Number 
                 Reserved 
                 Fixed 
               
             
          
           
               
                 2 
                 (MSB) 
               
               
                 3 
                 Transfer Length 
               
               
                 4 
                 (LSB) 
               
               
                 5 
                 Control 
               
               
                   
               
             
          
           
               
                 Fixed: 
                 0 = return one variable length block with length in bytes 
               
               
                   
                 specified by the Transfer Length 
               
               
                   
                 1 = return the number of fixed length blocks specified by 
               
               
                   
                 the Transfer Length; Block length is specified in the 
               
               
                   
                 the Mode Select command. 
               
             
          
         
       
     
     The above systems and methods can thus improve existing backup system efficiency and ease of use. While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others.