Simply describe the raid level:

A simple description of RAID level: RAID 0 is two disk read and write, if a bad so the data is all lost; RAID 1 is a piece of writing, a piece for backup, bad piece does not matter; Raid 2, 3, 4 are not used; The most common are RAID 5 and RAID 6, RAID 5 allows bad disk, but minimum Three disk to do, the capacity is N-1 capacity (equivalent to write a check information), RAID 6 allows bad 2 disk, but a minimum of four disks, the capacity is N-2 (equivalent to two disk check);

first, RAID technical specification Introduction RAID technology primarily includes raid0~raid 7 and other specifications, their focus is different, common specifications are as follows: RAID　　  0: RAID0 split data sequentially in bits or bytes, parallel read/It is written on multiple disks and therefore has a high data transfer rate, but it has no data redundancy and is therefore not considered a real raid structure. RAID 0 simply improves performance and does not guarantee the reliability of the data, and one of the disk failures will affect all data. 　　Therefore, RAID 0 cannot be applied to situations where data security requirements are high. RAID 1 : It implements data redundancy through disk data mirroring, generating data that is backed up on paired independent disks. When raw data is busy, data can be read directly from the mirrored copy, so RAID 1 can improve read performance. RAID 1 is the highest unit cost in a disk array, but provides high data security and availability. 　　When a disk fails, the system can automatically switch to read and write on the mirrored disk without having to reorganize the failed data. RAID  0+1 : Also known as the raid 10 standard, is actually a combination of RAID 0 and RAID 1 standard product, in a continuous split data in bits or bytes and parallel read/while writing multiple disks, make disk mirroring redundant for each piece of disk. 　　It has the advantage of having RAID 0 at the same time with the extraordinary speed and RAID 1 data high reliability, but the same CPU usage is also higher, and the disk utilization ratio is low. RAID 2: The data is striped across different hard disks, in bits or bytes, and is used to provide error checking and recovery using coding techniques called "Weighted average error correction code (cleartext)". 　　This coding technique requires multiple disk storage checks and recovery information, making RAID 2 technology more complex to implement and therefore rarely used in a business environment. RAID 3: It is very similar to Raid 2, where data is striped across different hard disks, except that RAID 3 uses simple parity and holds parity information with a single disk. If a disk fails, the parity disk and other data disks can regenerate the data, and if the parity disk fails, it does not affect data usage. 　　RAID 3 provides a good transfer rate for large amounts of continuous data, but for random data, parity disks can be a bottleneck for write operations. RAID 4: RAID 4 also tiles and distributes data across different disks, but the bars are in blocks or records. 　　RAID 4 uses a single disk as the parity disk, and each write operation requires access to the parity disk, where the parity disk becomes the bottleneck of the write operation, so RAID 4 is rarely used in a commercial environment. RAID 5: RAID 5 does not specify a single parity disk, but instead accesses data and parity information across all disks. On RAID 5, the read/write pointer can operate against a list of devices at the same time, providing higher data traffic. RAID 5 is more suitable for small data blocks and random read and write data. The main difference between RAID 3 and RAID 5 is that RAID 3 involves all array disks for each data transfer, whereas for RAID 5, most data transfers operate on only one disk and can be performed in parallel. There is a "write loss" in RAID 5, that is, each write operation will produce four actual read/write operation, where two reads the old data and the parity information, two times writes the new data and the odd and even information. RAID 6: Raid 6 Adds a second independent parity information block compared to RAID 5. Two independent parity systems use different algorithms, and the data is very reliable, even if two disks fail at the same time without affecting the use of the data. However, RAID 6 requires more disk space allocated to parity information and a greater write loss than RAID 5, so "write performance" is very poor. 　　Poor performance and complex implementations allow RAID 6 to be rarely used in practice. RAID 7: This is a new RAID standard, with its own intelligent real-time operating system and software tools for storage management, can be completely independent of the host running, do not occupy the host CPU resources. RAID 7 can be seen as a storage computer (Storage computer), which differs significantly from other RAID standards. In addition to the various criteria above (table 1), we can0+1 to build the required RAID array with multiple RAID specifications, such as raid5+3(RAID -) is a widely used array form. Users typically have the flexibility to configure disk arrays to obtain more disk storage systems that meet their requirements.

Initially, the RAID scheme is primarily for SCSI hard disk systems, and the system costs are more expensive. In 1993, Highpoint introduced the first Ide-raid control chip, which was able to use relatively inexpensive IDE hard drives to build a RAID system, greatly reducing the "threshold" of raid. Since then, individual users have also begun to focus on this technology, as hard drives are the most "slow" and least secure device in modern personal computers, and the data that users store in them is often far more expensive than the computer itself. With relatively little spending, RAID technology can enable individual users to enjoy multiple disk speeds and higher data security, and now the Ide-raid control chips in the PC market are mainly produced by Highpoint and promise, In addition, there are a subset of AMI companies (see table 2). Ide-raid chips for individual users generally provide support for RAID specifications such as RAID 0, RAID 1, and RAID 0+1 (RAID 10), although they are technically not comparable to commercial systems, but are sufficient for average users to provide speed improvements and security assurances. With the continuous improvement of the transmission rate of the hard disk interface, Ide-raid chip has been constantly updated, the chip market mainstream chip has all supported the ATA 100 standard, and Highpoint Company's new HPT 372 chip and promise the latest PDC20276 chip, You can even support the ATA 133 standard IDE hard drive. 　　In the motherboard manufacturers competition intensified, personal computer user requirements gradually improved today, on the motherboard on board raid chip manufacturers have a few, users can not purchase RAID card, directly set up their own disk array, feel the speed of the disk two. How to implement IDE raid via hardware control chip In the raid family, RAID 0 and RAID 1 are the most widely used on personal computers, and, after all, there are few individual users willing to use 4 or more hard drives to build RAID 0+1 or other hard disk arrays, so we're only going to explain these two types of raid here. We choose to support the Ide-raid function of the upgrade Kt7a-raid motherboard, step by step to introduce you ide-raid installation. 　　The Kt7a-raid is integrated with the Highpoint 370 chip, which supports RAID 0, 1, and 0+1. RAID 0 and RAID 1 do not require a disk, RAID 1 (Mirror) disk mirroring typically requires two (or more) hard disk drives to match, while RAID 0 (Striping) disks do not generally have this requirement, of course, It is ideal to choose a hard disk with similar capacity or even the exact same performance. For the convenience of testing, we use two blocks of 60GBCzech cool fish Ⅳ hard drive (Barracuda Ataⅳ, numbered st360021a).　System Selection Duron 750MHz CPU,2X128MB Wind Gold bar SDRAM, Geng GeForce2 Pro graphics card, should be said to be more general configuration, we also want to understand the need to build a RAID system requirements. 1.RAID 0 Creation The first step is to back up the data on the hard drive. Many users do not pay much attention to backup, especially to some of the more careless individual users. Creating a raid is a risky operation for data, and it can potentially ruin the entire hard drive's data, which is more the case with raid 0, which is the first to be introduced, and the data on all the disks in the array will be erased when the raid 0 o'clock is created, including the hard disk partition table. Therefore, it is important to have a Windows 98 Startup disk with the FDISK and Format command ready for this step first. The second step is to set the jumper of the two HDD to master, respectively, the IDE3 and IDE4 ports of the Kt7a-raid (they are controlled by the HighPoint370 chip on the motherboard). Since RAID 0 rebuilds the partition table for the two hard drives, we don't need to consider the order of the hard drive connections (as we'll see in the order of creating a RAID 1 o'clock in the following section). The third step is to set the BIOS to open the ATA RAID CONTROLLER. We enter the integrated peripherals option in the BIOS of the upgrade Kt7a-raid motherboard and turn on the ATA100 RAID IDE CONTROLLER. Upgrade recommended to change the boot sequence to ATA RAID, we found that in the system installation process is not feasible, is not the partition of the hard disk can be started? So we still set the floppy drive as a preference. 　　　The fourth step of the next step is to create the core of RAID 0, we illustrate to you in detail: 1. When the system BIOS setting is complete, reboot the computer and the hard drive will not be reported again when the boot is detected. 　　　2. The management of the disk will be taken over by the Highpoint 370 chip. 　　　3. The following is a very critical Highpoint 370 bios setting, press "Ctrl" and "H" at the same time in the Highpoint 370 disk scanning interface. 　　　4. The first thing to do after entering the Highpoint 370 BIOS setup interface is to select "Create RAID" for raid creation. 5. Choose the raid mode in "array mode", where you can see the options for RAID 0, RAID 1, RAID 0+1 and span, where weA RAID 0 item was selected. 　　　6.RAID mode selection is completed automatically exit to the previous menu for "Disk Drives" selection, generally speaking directly to the line. 7. The next setting is the stripe unit size, the default value is 64kB, no special requirements can be ignored. 8. Then "Start create" option, before you press "Y", please think seriously whether there is still important data left on the hard disk, this is your last chance! 　　　Once the raid is started, all data on the hard disk will be erased. 　　　9. Once the creation is complete, specify the boot boot disk and choose one of the following. 　　　Press "ESC" key to exit, of course, press "Y" to confirm. Highpoint 370 BIOS does not provide similar "Exit without Save" function, after modifying the settings is irreversible fifth step   Restart the computer again, we can see on the screen "Striping (RAID 0) for Array #0" The words. Insert the previously created boot disk and start the DOS. Open the Fdisk program, eh? How is a hard drive visible? Yes, the RAID array is considered to be a hard disk, and for the operating system, RAID is completely transparent and we do not have to worry about the management of the raid disk, which is done by the control chip. Next, according to ordinary single-drive method partition, you will find "this" hard disk capacity "changed" big, careful calculation, yes, the total capacity is two pieces of hard disk added capacity! We can compare the read and write of RAID 0 to a zip, which separates data on two hard drives, reads data faster and does not waste disk space. Don't forget to activate the primary partition after partitioning and formatting. The sixth step to select the operating system makes us quite a hassle, HighPoint370 chip provides driver support for WINDOWS98/NT/2000/XP, considering that the raid feature is targeted to relatively advanced users, we have chosen to support better Windows XP for new hardware Professional English version (using the English version of the system is mainly for the convenience of the back of the WinBench test, we use the raid completely can use the Chinese version of the operating system), Windows 2000 is also a good choice, but the hardware support is obviously less than the Windows XP Professional. The seventh step for the use of RAID computers, operating system installation and the general situation is not the same, let us look at the diagram, this is the first step of Windows XP "file copy" after the restart of the screen, the installer will be prompted in English "press F6 install SCSI device or RAID disk", This is a short process and users tend toIgnore the tips below the screen. 　　After pressing F6, the installation option appears, select "S" will install the raid control chip driver, select "Enter" is not installed. Pressing the "S" key will prompt you to insert the RAID chip driver disk. 　　Type Enter, the installer automatically searches the driver disk program, select "WinXP" that one and enter. If the version provided is inconsistent with the built-in driver version of Windows XP profesional, the installer prompts the user to make a selection. Press "S" to install the drive provided by the floppy disk and press "Enter" to install   Windows XP Professional. Press "S" and then need to confirm, this time is to press "Enter" (This ...) Confirm too much, hehe). 　　The next is a normal system installation, no difference from normal installation. The installation settings for RAID 0 are described here and we will talk about RAID 1 installation. RAID 1 has a much simpler installation than RAID 0 and is not disruptive in the right way. The creation of 2.RAID 1 is completely different in principle from RAID 0, but the installation setup process for RAID 1 is not much different from RAID 0, the main difference being the Highpoint 370 BIOS settings. To avoid duplication, we will only highlight this part of the setup: After entering the Highpoint 370 bios, select "Create RAID" for creation: 1. Click Enter on "Array mode" and select the second item in the RAID mode selection "Mirror (RAID 1) 　　　For data Security (create a mirror for the source disk). 　　　2. Next is the choice of the source disk, we remind the user again: Be careful, do not choose the wrong. 　　　3. Then the choice of the target disk, which is what we call the mirror disk or backup disk. 　　　4. Then start creating. 　　　5. After the creation, the BIOS will prompt for the image production, which is a very long process. 6. It took us about 45 minutes to complete the image production of 60GB, when RAID 1 was created. RAID 1 will copy the data from the primary disk to the mirror disk, so you need to be particularly careful when building RAID 1 o'clock, never mix the main disk with the mirror Panlong, otherwise the result will be tragic. RAID 1 can be created on two hard drives with no data, and can be added on a hard drive with an operating system installed, much more convenient than RAID 0 (except for the lengthy image production process). 　　After creation we tried to unplug one of the hard drives, HighPoint370 bios gave a warning, press "ESC", another hard disk to assume the responsibility of the source disk, all the data intact. ForTo add RAID 1 on a hard disk that already has an operating system installed, we recommend that you open the control chip in the BIOS → start the operating system installation Highpoint 370 drive → shut down the source disk and the mirror disk to the IDE3, 4 ports → enter Highpoint 370 　　BIOS setup RAID 1 (steps described above) → Restart the system to complete the creation. We tested the two types of raid in a simple way, although the test scores of RAID 0 were somewhat confusing, but the actual use still felt a lot faster than a single drive, especially when Windows XP Professional started abnormally fast and the progress bar flashed. As for the instability of the transmission rate curve, we estimate that there are some relationships with the platform selection, after all, the integrated chip is very susceptible to interference when it comes to this high data throughput. But even so, we saw that the data transfer rate of the raid 0 system reached a very high level, once close to 60mb/s. Compared to RAID 0, the performance of the RAID 1 system was not significantly improved relative to the single-disk system, but we found that the work curve of RAID 1 appeared to be very stable and rarely fluctuating in the test. 　　Look at the disk test scores in WINBENCH99 2.0 at a glance. For users and operating systems, RAID 0 and 1 are transparent and do not affect any operation, as we do with a hard disk. 　　Third, using the software method to achieve raid  in addition to using a RAID card or a chip on the motherboard to implement the disk array, we can use the software in some operating systems to implement the RAID function directly, such as Windows 2000/XP built-in RAID capabilities. 　　Before looking at the software RAID feature of Windows 2000/XP, let's look at a feature in Windows 2000-dynamic Disk Management. Dynamic disks, compared to the basic disk, are no longer used in the previous partitioning method, but rather called volume sets, which are in fact consistent with the partition, but with the following differences: 1. Can change disk capacity without restarting the disk size, without losing data, The basic disk will lose all the data if it wants to change the partition capacity (there are some special disk utility software that can change the partition without destroying the data, such as pqmagic, etc.). 2. Limits on disk space dynamic disks can be extended to disk space that is not contiguous, and you can create volume sets that span disks and combine several disks into a single large volume set. The partition of the basic disk must be a contiguous space on the same disk, and the maximum capacity of the partition is, of course, the capacity of the disk. 3. Volume set or number of partitions the number of volume sets that a dynamic disk can create on one disk is unlimited, and the relative basic disk can be up to 4 on a diskZone, and you can only divide one primary and extended partition when using DOS or Windows 9X. 　　* It's important to note that dynamic disks can only be used in Windows NT/2000/XP systems, and other operating systems do not recognize dynamic disks. Because most of the users ' disks are basic disk types, in order to use the Software RAID feature, we must convert them to Dynamic disks: Control Panel → administrative tools → Computer Management → Disk Management, switch one of the windows to a list of disks in the View menu. In this case, we can convert the selected disk to a dynamic disk via the right-click menu. 　　There are several types of dynamic volumes that you can see when you divide dynamic volumes. 　　1. Simple volume: Contains disk space on a single disk, as well as partition functionality. 　　(when there are two or more dynamic disks in the system and unallocated space on all two disks, we can choose between the following two types of volumes) 2. Spanned volumes: spanned volumes merge unallocated space from multiple disks into a single logical volume. 　　3. Striped Volume: Combines multiple (2 to 32) unallocated space on the disk to a volume. (We'll see another partitioning method if the two dynamic disks in the system are identical as described above) 4. Mirrored volumes: Two copies of the same volume, each on a single hard disk. 　　That's what we often call RAID 1. When we have three or more dynamic disks, we can use a more complex RAID mode of--raid 5, where new sub-volumes appear in the sub-volume interface. 　　5.RAID 5 Volume: the equivalent of a striped volume with parity, which is the RAID 5 mode. For most PC users, building RAID 0 is the most cost-effective form of array, so we're only going to talk about the build of software RAID 0 here: To use software RAID in Windows 2000/XP 0, you must first convert the disks that are ready to be included in the array to the dynamic disks described above (note that the default Disk Management interface for Windows 2000/XP is not able to convert basic and dynamic disks, refer to the description above), where we try to use the zoning of partitions, This is also the difference between software RAID and the use of RAID chips to build a disk array. We have selected a 29GB partition to divide the striped volume, when dividing the striped volume area, the system will require a corresponding partition, that is, the other dynamic disk must have the same 29GB or more unallocated space, after the allocation of striped volumes, two volumes of the same size will be merged by the system, 　　At this point, our formatting and other operations are also performed on two disks at a time. After the raid 0 was built, we decided to test its hard drive transfer rate to determine the performance improvement of this software RAID, and the platform we built for software RAID was not the same as the hardware RAID platform in the previous article.In order to ensure the performance of our software RAID, we adopted a higher-end system: Athlon XP 1700+, Samsung 256MB DDR memory, ASUS A7V266-E Motherboard, due to the low requirements of software RAID on hard disk specifications, 　　So the hard drive system we use different specifications of the hard disk, Seagate cool fish Ⅳ60GB and western data 1200BB 120GB two hard drive. In the second half of the transmission curve, we clearly saw that the software RAID 0 had a hard drive transfer rate of 60mb/s, completely exceeding the transmission rate of any of the drives in the array, and the benefits of RAID 0 began to manifest. 　　For the pursuit of high-performance users, this should be their dream. It should be explained that in the Linux environment, we can also use the Raidtools tool to implement the software RAID function. This tool can make a variety of disk arrays such as soft RAID 0, RAID 1, RAID 4, and RAID 5. Before using Raidtools, first determine whether the Linux core currently in use supports MD. If the core you are using is 2.0.X, and you are not compiling it yourself, in most cases it supports soft raid. 　　If you are unsure, you need to compile the core yourself. While RAID capabilities can give us a better speed experience and data security, it should be noted that most of the inexpensive ide-raid solutions in the market are still essentially "semi-soft" raid, only the raid control information is integrated in the raid chip, Therefore, the CPU utilization ratio is large, and the performance is not very stable. 　　This is also why the performance of software RAID 0 can sometimes exceed the "hardware" RAID 0 scenario in high-end systems. For users, the high-performance ide-raid storage System, or the need for more powerful CPU computing power, or the need for more expensive RAID cards, therefore, the disk array should still be considered more high-end applications. 　　But for beginners, using a simple and inexpensive disk array to improve the availability of computer data or to improve storage speed is also a good choice, of course, its performance is far from the high-end system compared. In short, we see a growing number of RAID architectures in the market, especially in the low-end market, the increasingly popular cheap ide-raid solution and hard drive prices are looking at each other, it seems to indicate the future development of personal data storage, let's wait and saw Highpoint 370 The BIOS does not provide a function similar to "Exit without Save", which is irreversible after the settings have been modified.

Simple description of RAID level: