Oracle remote disk image

Oracle remote Disk Mirroring is often encountered when learning Oracle. Here we will introduce how to solve the Oracle remote Disk Mirroring problem. Oracle remote Disk Mirroring Technology can adopt asynchronous methods to reduce network latency and impact on production systems. However, using this method for Oracle database images has a potential problem: the write-order consistency of the write operation sequence cannot be ensured. This increases the possibility of bad data blocks. In the worst case, the backup database may fail to be opened.

Data Guard transmits log files related to business logic integrity based on the logic level. Data Guard is based on the log file as the boundary. It will automatically check the integrity of the log file, and can check the log gap detection of the breakpoint log file), and automatically re-transmit the breakpoint log file through the FAL background process. Therefore, the consistency of the backup database is guaranteed.

Network Transmission Volume Analysis

The amount of network transmission is directly related to the feasibility of Disaster Tolerance solution implementation. In principle, Data Guard only transmits a log file, while Disk Mirroring Technology transfers all changed files, such as Data files, online logs, archived logs, and control files. For example, for transaction processing, Data Guard only transmits the log information of the corresponding DML statement, while Disk Mirroring Technology transfers all Data blocks involved in the exchange, as well as archive logs. According to statistics, the network transmission volume of Disk Images is seven times that of Data Guard, and the disk I/O frequency is 27 times that of Data Guard.

Take a banking business system as an example: When the daily transaction volume of the system reaches the peak, the log file will have 60 GB, and the network transmission rate must be 6 Mbps/second. With the Disk Mirroring Technology, the network transmission rate is at least 6 × 7 = 42 Mbps/second. If you also need to consider the reuse of lines by DB2, CICS, MQ, and other systems, and the expansion of the system, even if the 155Mbps line is used, from the consideration of the wide area network construction and operation costs, it is also difficult to implement database disaster tolerance using disk images.

Remote Disaster Recovery Analysis

Oracle remote disk image technology is limited by the underlying communication technology optical fiber, ESCON, and so on), generally there are distance restrictions, such as dozens or hundreds of kilometers, If You Want To implement Oracle remote disk image on the WAN, A large number of Network Relay and forwarding devices are required. In this way, the investment of network devices will increase greatly, and the increase of network latency will also affect the production system.

In contrast, Data Guard transmits Data based on Oracle Net Services (standard TCP/IP protocol. TCP/IP is the transfer protocol on ESCON. Because it is more optimized in information packet forwarding, routing, and congestion control, at the same time, TCP/IP has nothing to do with the underlying communication protocol, such as Ethernet, ATM, and SONET. Moreover, TCP/IP can transmit several packets in parallel. Therefore, TCP/IP is more efficient and has lower network latency, and has less impact on the production system.

Data protection Capability Analysis

Among all kinds of faults, the highest failure rate is disk failure uption ). In the case of bad disk blocks, the Disk Mirroring Technology will faithfully spread this error to the disk of the backup database, leading to the unavailability of the backup database. Because Data Guard transfers log files and verifies the integrity of log files before transmission, it is impossible to have physical bad blocks or disk controller Faults due to system disks, writing data blocks badly leads to bad blocks in the backup database.

ROI) Analysis

The Data Guard software has no special requirements on hardware. The network only requires TCP/IP. Backup databases can be built on low-end systems and inexpensive disk arrays. The Disk Mirroring Technology requires not only buying expensive Disk Mirroring software separately, but also demanding hardware requirements.

In addition, Data Guard provides the query statistics function for the backup database, while the backup database created by Disk Mirroring Technology is normally idle and can be applied only when a fault occurs; to reduce the load on the production database, Data Guard can also port the physical backup function to the backup database to back up the physical backup Data generated by the database. It can also be used for recovery operations on the production database. The preceding section describes Oracle remote disk images.

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