Electrical computers and digital processing systems: memory – Storage accessing and control – Memory configuring
Reexamination Certificate
2001-11-30
2004-06-01
Sparks, Donald (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Memory configuring
C711S121000, C710S022000, C707S793000
Reexamination Certificate
active
06745310
ABSTRACT:
FIELD
The present invention relates generally to memory systems, and more particularly to an apparatus and method for providing real-time local and remote management of the memory system that optimizes maintenance and backup operations while reducing overhead on a data processing network and attached data processing systems.
BACKGROUND
Computers are widely used for storing, manipulating, processing, and displaying various types of data, including financial, scientific, technical and corporate data, such as names, addresses, and market and product information. Thus, modern data processing systems generally require large, expensive, fault-tolerant memory or data storage systems. This is particularly true for computers interconnected by networks such as the Internet, wide area networks (WANs), and local area networks (LANs). These computer networks already store, manipulate, process, and display unprecedented quantities of various types of data, and the quantity continues to grow at a rapid pace.
Several attempts have been made to provide a data storage system that meets these demands. One, illustrated in
FIG. 1
, involves a server attached storage (SAS) architecture
10
. Referring to
FIG. 1
, the SAS architecture
10
typically includes several client computers
12
attached via a network
14
to a server
16
that manages an attached data storage system
18
, such as a disk storage system. The client computers
12
access the data storage system
18
through a communications protocol such as, for example, TCP/IP protocol. SAS architectures have many advantages, including consolidated, centralized data storage for efficient file access and management, and cost-effective shared storage among several client computers
12
. In addition, the SAS architecture
10
can provide high data availability and can ensure integrity through redundant components such as a redundant array of independent/inexpensive disks (RAID) in data storage system
18
.
Although an improvement over prior art data storage systems in which data is duplicated and maintained separately on each computer
12
, the SAS architecture
10
has serious shortcomings. The SAS architecture
10
is a defined network architecture that tightly couples the data storage system
18
to operating systems of the server
16
and client computers
12
. In this approach the server
16
must perform numerous tasks concurrently including running applications, manipulating databases in the data storage system
18
, file/print sharing, communications, and various overhead or housekeeping functions. Thus, as the number of client computers
12
accessing the data storage system
18
is increased, response time deteriorates rapidly. In addition, the SAS architecture
10
has limited scalability and cannot be readily upgraded without shutting down the entire network
14
and all client computers
12
. Finally, such an approach provides limited backup capability since it is very difficult to backup live databases.
Another related approach is a network attached storage (NAS) architecture
20
. Referring to
FIG. 2
, a typical NAS architecture
20
involves several client computers
22
and a dedicated file server
24
attached via a local area network (LAN
26
). The NAS architecture
20
has many of the same advantages as the SAS architecture
10
including consolidated, centralized data storage for efficient file access and management, shared storage among a number of client computers
22
, and separate storage from an application server (not shown). In addition, the NAS architecture
20
is independent of an operating system of the client computers
22
, enabling the file server
24
to be shared by heterogeneous client computers and application servers. This approach is also scalable and accessible, enabling additional storage to be easily added without disrupting the rest of the network
26
or application servers.
A third approach is the storage area network (SAN) architecture
30
. Referring to
FIG. 3
, a typical SAN architecture
30
involves client computers
32
connected to a number of servers
36
through a data network
34
. The servers are connected through separate connections
37
to a number of storage devices
38
through a dedicated storage area network
39
and its SAN switches and routers, which typically use the Fibre Channel-Arbitrated Loop protocol. Like NAS, SAN architecture
30
offers consolidated centralized storage and storage management, and a high degree of scalability. Importantly, the SAN approach removes storage data traffic from the data network and places it on its own dedicated network, which eases traffic on the data network, thereby improving data network performance considerably.
Although both the NAS
20
and the SAN
30
architectures are an improvement over SAS architecture
10
, they still suffer from significant limitations. Currently, the storage technology most commonly used in SAS
10
, NAS
20
, and SAN
30
architectures is the hard disk drive. Disk drives include one or more rotating physical disks having magnetic media coated on at least one, and preferably both, sides of each disk. A magnetic read/write head is suspended above each side of each disk and made to move radially across the surface of the disk as it is rotated. Data is magnetically recorded on the disk surfaces in concentric tracks.
Disk drives are capable of storing large amounts of data, usually on the order of hundreds or thousands of megabytes, at a low cost. However, disk drives are slow relative to the speed of processors and circuits in the client computers
12
,
22
. Thus, data retrieval is slowed by the need to repeatedly move the read/write heads over the disk and the need to rotate the disk in order to position the correct portion of the disk under the head. Moreover, hard disk drives also tend to have a limited life due to physical wear of moving parts, a low tolerance to mechanical shock, and significantly higher power requirements in order to rotate the disk and move the read/write heads. Some attempts have been made to rectify these problems including the use of cache servers to buffer data written to or read from hard disk drives, redundant or parity disks as in RAID systems, and server clusters utilizing load balancing with mirrored hard disk drives. However, none of these solutions are completely satisfactory. Cache servers only improve perceived performance for static data stored in cache memory. They do not improve performance for the 40 to 50 percent of data requests that result in cache misses. RAID configurations with their multiple disk drives are also subject to mechanical wear and tear, as well as head seek and rotational latencies or delays. Similarly, even server clusters with load balancing switches are helpful only for multiple read access; write access is not improved. Moreover, cluster management also adds to the system overhead, thereby reducing any increased performance realized.
As a result of the shortcomings of disk drives, and of advancements in semiconductor fabrication techniques made in recent years, solid-state drives (SSDS) using non-mechanical Random Access Memory (RAM) devices are being introduced to the marketplace. RAM devices have data access times on the order of less than 50 microseconds, much faster than the fastest disk drives. To maintain system compatibility, SSDs are typically configured as disk drive emulators or RAM disks. A RAM disk uses a number of RAM devices and a memory-resident program to emulate a disk drive. Like a disk drive a RAM disk typically stores data as files in directories that are accessed in a manner similar to that of a disk drive.
Prior art SSDs are also not wholly satisfactory for a number of reasons. First, unlike a physical hard disk drive, a RAM disk forgets all stored data when the computer is turned off. The requirement to maintain power to keep data alive is problematic with SSDs that are generally used as disk drive replacements in servers or other computers. Also, SSDs do not presently provide the high densities and large memory capacitie
Chow Yan Chiew
Hsia James R.
Chace Christian P.
Dorsey & Whitney LLP
Sparks Donald
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