The recognition of tape backup involves two issues, one is why it should be backed up, and the second is why the tape is selected. Let's first look at the first question.
large natural disasters, small theft, power outages and even the casual operator errors, will affect the normal operation of the system, and even cause the system completely paralyzed. The task and significance of backup is to recover a ready-to-use system quickly, simply and reliably through data backup after a disaster. Of course, there are still many misunderstandings about backup. These misunderstandings have caused some users to replace backup schemes with other storage schemes. One
misunderstanding, some users believe that the backup copy is, in fact, can not make copies of data files leaving history to do track, you can not leave the system information such as NDS or the Registry. Complete backup includes the full restoration of data management and system automation, in this sense, the backup = copy + management;
misunderstanding of the two, in order to replace the backup hardware backup. Although many servers have adopted a fault-tolerant design, that is, hard disk backup (dual hot backup, disk array and disk image). But these are not good backup solutions. For example, in dual-hot backup, if two devices fail at the same time, the whole network will be paralyzed; //This article is quoted from www.45it.com computer software and hardware application network
Misunderstanding 3, only for data files Backup. Some people think that backup is just a backup of data files, system files and applications do not need to be backed up, because they can be reinstalled through the installation disk. In fact, it may take several days for the installation to re-set various parameters and addresses. The most effective backup is to back up the entire network system. So what
storage technology should be chosen to back it? Among the major technologies of storage, chip storage, disk, optical storage, and tape storage, the latter three have already achieved high capacity, and it seems that they can all serve as backup technologies. But considering the unit cost and high capacity, only tape technology is really suitable for data storage backup. In fact, tape technology has long been the only data storage backup technology of choice. Tape media not only provides high capacity, high reliability, and manageability, but also costs much less than optical discs and disks (the unit cost is less than 10% of the disk).
You must know that backup is to prevent natural disasters, virus intrusion, vandalism, etc., so the frequency of using backup data is not very high, the access speed of backup data is not a very important factor, users are not necessary In order to pursue an unimportant high speed, the investment is doubled. However, the capacity of storage media has the primary importance in backup.
hardware technology and products
hardware technology including magnetic tape drive technology and media technology. Based on the same technology, different manufacturers have developed different products. These products will vary in the mechanical part, but generally ensure read compatibility under the same technology. Our product list in the post will help readers have a preliminary understanding of the industry's mainstream tape products, but the table does not make accurate comparisons. Tape drive according
technology can be divided into two broad categories, linear and helical scan technology techniques. Linear technology originated from analog audio recording technology, which records data by touching a single or multiple static heads with high-speed moving tape. It is further divided into QIC (Quarter-Inch-Cartridge, 1/4 inch) and 1/2 inch according to the width of the tape. The former has a DC2000/Travan tape drive, but the scenery is no longer. The 1/2-inch tape drive is a multi-head read/write system with a high data transfer rate and a large capacity. Representative products are DLT, 3480/3490, etc.
The spiral scanning technology originated from the analog video recording technology. It is opposite to the data stream technology. The tape is wound around the drum, the tape moves very slowly, and the drum rotates at high speed on both sides of the drum. The head also scans the tape at high speed for recording.
Mammoth (8mm), AIT (8mm) and DAT (4mm) is one of the representatives, 4mm of the DAT roadmap to DDS-4 only. Mammoth is Exabyte's exclusive technology that increases tape strength to improve read and write speed and reliability. Recently, Exabyte also introduced VXA technology developed from DDS. AIT is an open smart tape drive standard developed by Sony that enhances search performance.
latest LTO (Linear Tape Open- Linear Tape-Open) technology is a combination of tape storage technology linear multi-channel bi-directional tape formats. The LTO fourth-generation standard has a capacity of 800G and a transmission speed of 80MB/s to 160MB/s, which represents the development direction of tape technology. According to the reporter, the so-called HP and IBM LTO products are not compatible with the inaccurate news. At least they are read compatible.
tape media can be divided into MP (metal particle), AME (metal evaporated tape), DAT, DLT like. Different drive technologies may also use the same media technology. For example, IBM LTO and SDLT use MP media, and AIT-3 and Mammoth use AME media. Even in the same series of upgrades, long-term use of non-default media to read data is very harmful to tape.
All these products through market segmentation have made their position.
Backup Strategy
The choice of tape products is closely related to the user's backup strategy. Let's first look at several elements of the backup strategy.
Full Backup is a full backup of the entire system, including systems and data, with a single tape per day. The advantage of this type of backup is that you can recover lost data with just one tape. However, it also has its shortcomings. First, a large amount of backup data is duplicated. Second, because the amount of data that needs to be backed up is quite large, the backup takes a long time.
Incremental Backup means that each backup data is only new and modified compared to the last backup. The advantage of this type of backup is obvious: there is no duplicate backup data, but recovering data is cumbersome – you must reverse the recovery one by one.
differential backup (Differential Backup) is the data for each backup is increased relative to after the last full backup and modified data. Differential backups have all of their advantages while avoiding the shortcomings of the other two strategies. First of all, it does not need to do a full backup of the system every day, so the backup takes a short time and saves disk space; secondly, its disaster recovery is very convenient. The system administrator can recover the system by only two tapes, the full backup tape and the tape one day before the disaster.
Backup window is the time that can be used as a backup. Data backup can greatly affect the responsiveness of the server. Therefore, the backup system must choose the appropriate available backup time. Some systems and applications have strict requirements for backup windows.
understand these basic knowledge, users can roughly estimate the required indexes own products. The principle is that the capacity of a single tape must be greater than or equal to the sum of the capacity of the hard disk to be backed up. In addition, the performance of the tape drive itself must meet the needs of the backup window. Let's look at an example:
Assume that the total backup capacity is 500GB, and the working time is five days a week, using a full backup-incremental backup strategy. The backed up tape is required to remain online for two weeks. The backup window is 6 hours and there is no specific requirement for the recovery window. Usually incremental backups are calculated in 10% increments of data, according to the following backup formula:
Full backup + 4 incremental backups = one week backup data factor (100% + 4 × 10% increment = 1.4
Therefore, the amount of backup data for one week is: 500GB × 1.4 = 700GB, and the amount of backup data for two weeks is 1400GB.
Full backup work can be done on rest days, and differential backup work can be done at night. Since the backup job must be completed within a 6-hour backup time, this means that the amount of data backup per hour cannot be less than (in the worst case) 500/6=83GB. This is the rate that should be achieved when choosing a backup device.