What is a disk array?

Source: Internet
Author: User
Tags ide hard drive
Disk Arrays, short for RAID (redundantparrayspofpinexpensivepdisks), refer to "cheap and redundant disk arrays. The principle is to use arrays as disk groups and use them in combination with the Design of Distributed Data arrangement to improve data security. The disk array mainly targets hard disks. in terms of capacity and speed, it cannot keep up with the development of CPU and memory, and proposes improvement methods. A disk array is a large disk, which is made up of many Inexpensive Disks with low capacity, high stability, and slow speed, improve the efficiency of the entire disk system by using the bonus Effect of data provided by individual disks. At the same time, this technology is used to cut data into many segments and store them on various hard disks. P

The disk array can also use the concept of paritypcheck. When any hard disk in the array fails, the data can still be read. when the data is restructured, the data in the faulty hard disk will be written, after calculation, place the disk again.

Disk Array origin: P

The article "apcasepforpredundantparrayspofpinexpensivepdisks" was published by the University of Berkeley in 1987 ". In this article, we talked about the raid vocabulary and defined the raid Level 5. The goal of berclay University's research is to reflect the fast CPU performance at that time. CPU performance increases by about 30 ~ every year ~ 50%, while hard magnetic machines can only grow by about 7%. The research team hopes to find a new technology that will immediately increase the efficiency to balance the computing power of computers in the short term. At that time, the berclay research group focused on efficiency and cost. P

In addition, the research team also designed fault-tolerance and logicalpdatapredundancy, which produced the raid theory. At the beginning of the study, cheap (inexpensive) disks were also the main focus, but later found that a large number of cheap disk groups cannot be applied to the real production environment, and later inexpensive was changed to independence, many independent disk groups. P

Disk Array, current affairs trend: P

Since its own PC, hard disks are the most commonly used storage devices. However, in the entire computer system architecture, hard disk speed is one of the weakest devices in the PC compared with CPU and ram. Therefore, in order to accelerate the overall data traffic of the Computer, increase the storage throughput, and improve the security of hard disk data, the design of the disk array is appropriate. P

With the rapid development of technology, hard disk capacity has now reached more than 80 GB, speed to 20 thousand RPM, or even 25000 rpm, and the price is really cheap, coupled with the current popularity of enterprises, human resources planning (enterprisepresourcepplanning: ERP) is the main goal of every company to build a network. Therefore, using a local network to transmit data, the server's hard disk is very important. In addition to large capacity and fast speed, stability is a basic requirement. Because of this, disk arrays have been widely used on personal computers. P

There are three types of Disk Arrays: External disk array, internal disk array, and software simulation. External disk array cabinets are most often used on large servers, with the hotpswap feature, but these products are expensive. The internal disk array card is suitable for technical staff because it is cheap but requires high installation technology. In addition, the software simulation method is not suitable for servers with big data traffic because it will drag down the speed of the machine. P

As we can see from the above, the IDE disk array is now widely used. The stability and performance of the IDE interface hard disk have been greatly improved, coupled with cost considerations, therefore, using the IDE interface hard disk as the disk array's final solution is the best method.

In network storage, a disk array is a system that combines several hard disk drives according to certain requirements. The entire disk array is managed by the array controller. A tape library is a tape-based backup system like an automatic tape drive. It consists of multiple drives, multiple slots, and robotic arm, the mechanical arm can automatically disassemble and load the tape.

It provides the same basic automatic backup and data recovery functions, but also has more advanced technical features. It is also essential for network administrators to master the installation and operation of network storage devices.

When constructing a wireless LAN, install, debug, and use wireless LAN products such as routers, wireless network adapters, wireless network adapters, and antennas.

Mainstream structure of the disk array:
The disk array is directly connected to the host as an independent system outside the host or through the network. The disk array has multiple ports that can be connected to different hosts or ports. A host connects to different ports of the array to increase transmission speed.
As with the current integrated cache for a single PC disk, in order to speed up interaction with the host inside the disk array, there is a certain amount of buffer memory. The cache interaction between the host and the disk array, and the interaction data between the cache and the specific disk.
In applications, some common data needs to be read frequently. The disk array searches for frequently read data based on internal algorithms and stores the data in the cache, the speed for the host to read the data is accelerated. If the host does not read data from other caches, the array will directly read the data from the disk and transmit it to the host. For data written by the host, it is only written in the cache, and the host can immediately complete the write operation. Then, the cache writes data to the disk.

Disk Array Q &

1. What is a disk array )?
A disk array is a technology used by a hard disk controller to control the connection between multiple hard disks. This allows read/write synchronization between multiple hard disks, reduces errors, and increases efficiency and reliability.
2. What is raid?
Raid, short for Redundant Array of Inexpensive Disk, is a cheap redundant disk array, the objective is to reduce errors and improve the performance and reliability of the storage system. Common levels include 1, 3, and 5.
3. What is raid level 0?
Raid level 0 is the implementation of data striping technology. It forms a disk array for all hard disks and can read and write multiple hard disks at the same time, however, it does not have backup and fault tolerance capabilities. It is cheap and the hard disk is the most efficient to use, but the reliability is the worst.
Taking a raid level 0 disk array composed of two hard disks as an example, it writes 1st and 2 of data to the first hard disk, and the third and fourth places to the second hard disk ...... Similarly, it is called "Data splitting". Because the write operations of data on each disk are done at the same time, the storage speed can be several times faster than that of a single hard disk.
However, in this case, a hard disk on the disk array breaks down and stores the data in different hard disks as it breaks down the data integrity, without the backup tape of the entire disk array, all the data will be irrecoverable. Therefore, despite its high efficiency, few are risking data loss to use this technology.
4. What is raid Level 1?
Raid Level 1 uses the disk mirror (Disk ror ing) technology to replicate the content of one hard disk to another. Therefore, it is capable of backup and fault tolerance, in this way, the efficiency is not high, but the reliability is high.
5. What is raid Level 3?
Raid Level 3 uses byte-interleaving (Data staggered storage) technology. The hard disk operates simultaneously under the SCSI control card and stores the data used for parity verification in a specific hard disk, it is capable of fault tolerance. The efficiency of using a hard disk is to reduce the number of hard disks installed, and its reliability is better.
6. What is raid Level 5?
Raid Level 5 uses the Disk Striping technology. Unlike Level 3, raid Level 5 stores parity data in hard disks, each hard disk operates in parallel under the control of the SCSI control card and has fault tolerance capabilities. Like Level 3, its usage efficiency is also reduced after several installations.
7. What is a hot swapping hard drive?
Hot-swappable disk is an English name hot-swappable disk. In a disk array, if you use a hard disk that supports hot-swappable technology, the server does not need to be shut down if a hard disk breaks down, remove the broken hard disk and replace it with a new one. When a general commercial disk array breaks down the hard disk, it will automatically prompt the Administrator to change the hard disk.

Brief Introduction to raid Disk Array Technology

In the early stages of computer development, the price for "large-capacity" hard disks was quite high. The main solution to the security problem of data storage was to back up data using tape drives and other devices, this method ensures data security, but it is cumbersome to check and back up data. In 1987, the three engineers, Patterson, Gibson, and Katz, published a paper entitled A Case of Redundant Array of Inexpensive Disks at UC Berkeley, the basic idea is to combine multiple low-capacity, relatively cheap hard drive, so that its performance exceeds an expensive large hard disk. This design concept was quickly accepted. Since then, RAID technology has been widely used, and data storage has entered a new era of faster, safer, and cheaper.
Disk arrays are unfamiliar and mysterious to PC users. In the impression, the disk array seems to be stuck in such a scenario: In the wide hall, there are numerous cabinets, and several engineers with gloomy expressions and early approval are wandering in it, we will continue to extract heavy hard disks from them, and then insert heavy hard disks into the blocks ...... Finally, with the high capacity hard drive prices continue to decrease, personal computer performance continues to improve, IDE-RAID as the disk performance improvement of the cheapest solution, began to enter the general user computer system.

I. Introduction to raid specifications
RAID technology mainly includes RAID 0 ~ Raid 7 and other specifications have different focuses. common specifications include:

RAID 0: RAID 0 continuously splits data by bit or byte and reads/writes data on multiple disks in parallel. Therefore, RAID 0 has a high data transmission rate, but it has no data redundancy, therefore, it cannot be regarded as a real raid structure. RAID 0 only improves performance and does not guarantee data reliability. However, failure of a disk affects all data. Therefore, RAID 0 cannot be used in scenarios with high data security requirements.
Raid 1: it achieves data redundancy through disk data mirroring, and generates data backed up by each other on a pair of Independent Disks. When raw data is busy, data can be directly copied from the image, so RAID 1 can improve read performance. Raid 1 is the most costly disk array, but provides high data security and availability. When a disk fails, the system can automatically switch to the image disk to read and write data without restructuring the invalid data.
RAID 0 + 1: Also known as the raid 10 standard, it is actually a product that combines RAID 0 and RAID 1 standards, when data is continuously divided by bit or byte and multiple disks are read/written in parallel, the disk image is redundant for each disk. Its advantage is that it has both the extraordinary speed of RAID 0 and the high data reliability of RAID 1, but the CPU usage is also higher, and the disk utilization is relatively low.
Raid 2: Data is distributed in blocks on different hard disks, measured in bytes or bits, and the average error correction code (Hamming Code) is used) "encoding technology to provide error detection and recovery. This encoding technology requires multiple disks to store inspection and recovery information, making raid 2 more complicated and therefore rarely used in commercial environments.
RAID 3: similar to raid 2, RAID 3 blocks data on different hard disks. The difference is that raid 3 uses simple parity, use a single disk to store the parity information. If a disk is invalid, data can be re-generated on the parity disk and other data disks. If the parity disk is invalid, data usage will not be affected. RAID 3 provides a good transfer rate for a large amount of continuous data, but for random data, the parity disk will become the bottleneck of write operations.
Raid 4: Raid 4 also blocks data and distributes the data on different disks. However, the disk unit is block or record. Raid 4 uses a disk as the parity disk. Each write operation requires access to the parity disk. In this case, the parity disk becomes the bottleneck for write operations. Therefore, raid 4 is rarely used in commercial environments.
RAID 5: RAID 5 does not separately specify a parity disk. Instead, it accesses data and parity information across all disks. On RAID 5, read/write pointers can be performed on the array devices at the same time, providing higher data traffic. RAID 5 is more suitable for small data blocks and random read/write data. The main difference between RAID 3 and RAID 5 is that each data transmission of RAID 3 involves all array disks. For RAID 5, most data transmission only operates on one disk and can be performed in parallel. There is a "Write loss" in RAID 5, that is, each write operation will generate four actual read/write operations, two of which read the old data and parity information, write new data and parity information twice.
Raid 6: Compared with RAID 5, raid 6 adds a second independent parity information block. Two independent parity systems use different algorithms, and the data reliability is very high. Even if the two disks are invalid at the same time, the data usage will not be affected. However, raid 6 needs to allocate more disk space to the parity check information, which has a greater "Write loss" compared with RAID 5. Therefore, the "Write Performance" is very poor. Poor performance and complex implementation methods make raid 6 rarely applied in practice.
Raid 7: this is a new raid standard. It comes with an intelligent real-time operating system and a software tool for storage management. It can run completely independently of the host and does not occupy host CPU resources. Raid 7 can be viewed as a storage computer, which is significantly different from other raid standards. In addition to the above standards (such as table 1), we can combine multiple raid specifications like RAID 0 + 1 to build the required raid array, such as RAID 5 + 3 (RAID 53) it is a widely used array. Generally, you can flexibly configure disk arrays to obtain a more suitable disk storage system.
At the beginning, the raid solution mainly targets the SCSI hard drive system, and the system cost is relatively high. In 1993, highpoint company launched the first IDE-RAID control chip, can use relatively cheap IDE hard disk to build a RAID system, thus greatly reducing the raid "threshold ". Since then, individual users have begun to pay attention to this technology, because hard disks are the most "slow" and least secure devices in modern personal computers, the data stored by users often far exceeds the computer's own price. When the cost is relatively small, RAID technology can enable individual users to enjoy doubled disk speed and higher data security, the IDE-RAID control chips on the PC market are mainly from highpoint and promise, and some are from AMI companies (such as table 2 ).

IDE-RAID chips for individual users generally only support RAID 0, RAID 1 and RAID 0 + 1 (RAID 10) raid specifications, although they are technically incomparable with commercial systems, the speed improvement and security assurance provided by ordinary users are sufficient. With the continuous improvement of hard disk interface transmission rate, IDE-RAID chip is constantly updated, mainstream chip on the chip market has all supported the ATA 100 standard, highpoint's new HPT 372 chip and promise's latest pdc20276 chip can even support the ATA 133 standard IDE hard drive. In today's increasingly competitive motherboard manufacturers and increasingly demanding personal computer users, there are no fewer vendors that carry raid chips on the motherboard. users do not need to purchase raid cards, directly build your own disk array and feel the speed of the disk.
Ii. How to Implement ide raid through hardware control chip
In the raid family, RAID 0 and RAID 1 are most widely used on PCs, after all, there are few individual users who are willing to use four or more hard disks to build RAID 0 + 1 or other hard disk arrays, therefore, we will only explain the two raid methods here. We choose to support the upgrade IDE-RAID KT7A-R aid motherboard, step by step to introduce you to the installation of IDE-RAID. The upgraded KT7A-RAID integrates a highpoint 370 chip that supports RAID 0, 1, 0 + 1.

Hard Disks are indispensable for raid. RAID 0 and RAID 1 have different requirements on disks. Raid 1 (mirror) Disk Images generally require the same capacity of two or more hard disks, RAID 0 (striping) disks generally do not have this requirement. Of course, it is ideal to choose hard disks with similar capacity and performance or even completely the same. To facilitate the test, we have selected two 60 GB hard drives (barracuda ata IV and st360021a ). The system selects duron MHz CPU, 2 x mb of gold cord SDRAM, and upgrades geforce2 pro graphics card. It should be said that it is a common configuration. We also hope to learn about the system requirements for raid construction. 1. Create RAID 0
Step 1
First, back up the data in the hard disk. Many users do not pay attention to backup, especially some careless individual users. Creating raid is a dangerous operation for data, and data on the entire hard disk may be destroyed without any worries. We first introduce RAID 0. This is especially true when creating RAID 0, all data on the disk in the array will be erased, including the hard disk partition table. Therefore, you must first prepare a Windows 98 boot disk with the fdisk and format commands. This step is also important.
Step 2

Set the jumper of the two hard disks to the master and connect them to the ide3 and ide4 ports of the upgrade KT7A-RAID, which are controlled by the highpoint370 chip on the motherboard ). Since RAID 0 will recreate the partition tables of two hard disks, we do not need to consider the order of Hard Disk connections (we will see below that this order is important when creating RAID 1 ).
Step 3
Set the bios and enable the ata raid Controller. We enter the integrated peripherals option in the BIOS of the upgrade KT7A-RAID board and enable the ata100 raid ide controller. We recommend that you change the boot sequence to ATA 100 raid. Actually, we find that this is not feasible during system installation. Can a hard disk with no partitions be started? Therefore, we still set the soft drive as the preference.
Step 4

The next step is to create the core content of RAID 0. We will introduce it in illustration:
1. After the system BIOS settings are complete, restart the computer and no hard disk will be reported during boot detection.
2. disk management will be taken over by the Highpoint 370 chip.
3. The following are critical highpoint 370 BIOS settings. On the Highpoint 370 disk scan page, press Ctrl and h at the same time ".
4. Go to the Highpoint 370 BIOS settings page and select "create raid" to create a raid.
5. select the raid mode in "array mode". Here we can see the options for RAID 0, RAID 1, RAID 0 + 1, and span, select RAID 0 here.
6. After the raid mode is selected, the system automatically exits from the top menu and selects "disk drivers". Generally, press enter directly.
7. The next setting is the unit size of the band. The default value is 64 KB. You can ignore this setting without special requirements. 8. next is the "Start create (start to create)" option. Before you press "Y", please think about whether there is any important data on the hard disk. This is your last chance! Once raid is created, all data on the hard disk is cleared.
9. After the boot disk is created, specify one.
Press ESC to exit. Of course, Press Y to confirm.
Highpoint 370 BIOS does not provide a function similar to "exit without save". It is irreversible after modification.

How to Build raid

As a member of the storage device, the hard disk plays an extremely important role. Most of our data is stored through the hard disk. Today, we will have a deep understanding of the internal world of hard disks and learn how to install dual hard disks and raid disk arrays.
Explanation of Hard Disk
Although there are some differences between various hard disks in terms of the external structure, the internal structure is still similar. After all, the working method of hard disks will not change. After opening the hard disk shell, we can see the mysterious internal world. Its core parts include the disk body, spindle motor, read/write head, track motor, and other main components. However, we need to remind you that you should never open the shell of the hard disk at will, which will make the entire hard disk decommission 100%, because the internal disk of the hard disk cannot be contaminated with a grain of dust, otherwise it must be decommissioned. Generally, the maintenance of the internal structure of the hard disk must be carried out in a dust-free laboratory with extremely strict requirements.
1. Disk body
The disk is physically divided into four parts: disk, side, track, cylinder, and sector. The magnetic surface is the upper and lower sides of each disk. The first side of the first disk is 0, and the next side is 1. The first side of the second disk is 2, so on ....... A magnetic track is a number of concentric circles divided into disks during disk formatting. The number of tracks on the outermost layer increases progressively toward the center of the magnetic surface. In fact, the structure of the disk is very similar to that of a floppy disk. However, the disc is composed of multiple overlapping disc segments separated by washers, And the disc is made of metal disc (IBM used glass as the material), the surface is extremely smooth, and coated with magnetic substances.
2. read/write head components
The read/write head component consists of a read/write head, a drive arm, and a drive shaft. During operation, the head scans the disc with a specified radius through the drive arm and drive shaft to read and write data. The head is a combination of multiple heads made by the integrated process and adopts a non-contact structure. After the hard disk is powered on, the read/write head is relatively flying on the high-speed rotating disk surface, and the gap between the head and the disk surface is only 0.1 ~ 0.3 μm. The new MR (magnetoresistive heads) Magnetic Head adopts a read/write splitting head structure. The traditional magnetic induction head is used for write operations, while the MR head is used for read operations.
3. Head Drive Mechanism
For a hard disk, the head drive mechanism is like a commander who controls the reading and writing of the head and directly transmits commands to the drive arm and drive shaft. The head drive mechanism consists of a sound ring motor, a head drive car, and a anti-vibration mechanism. The head Drive Mechanism correctly drives the head and precisely locates the track specified by the system command in a short time to ensure the reliability of data reading and writing. Generally, the motor of the head mechanism includes three types: stepping motor, torque motor and audio ring motor. Currently, the hard drive is mostly driven by audio ring motor. The sound ring is a coil inserted in the middle with a magnetic rod connected to the head. When the current passes through the coil, the magnetic rod will be displaced, and then drive the car carrying the head, the head movement distance is obtained based on the information encoding of the Controller's head position on the disk to achieve accurate positioning.
4. Spindle Components
The spindle components of the hard disk are mainly bearings and motors. We can generally think that the bearing determines the noise performance of a hard disk, while the motor determines the performance. Of course, this is not completely true, But it basically expresses the importance of these two components in the hard disk. From ball bearings to oil-immersed bearings to liquid bearings, Hard Drive bearings are constantly being improved. At present, liquid bearings have become an absolute mainstream product with no direct friction between metals, in this way, in addition to extending the life of the spindle motor and reducing the fever, the most important thing is to achieve a breakthrough in hard disk noise control. However, it should be pointed out that the use of liquid bearings does not have any benefits for performance, but may even extend the seeking time. For PC devices, it seems that noise and performance are a conflict that is always difficult to balance.
Dual hard disk installation
With the popularization of broadband networks and multimedia technology, we have a growing demand for hard disk capacity. Under the temptation of various large software, video animation, and 3D games, many users are considering adding a hard disk. In fact, installing dual hard disks is not a hassle. Even if you have no experience, you can easily solve it with our help.
Currently, the mainstream motherboard provides at least one ide interface, and each ide interface can install two IDE hard disks. Before installing a dual hard disk, we must first set the jumper of the hard disk, because the Master/Slave Mode must be set at this time. Generally, the Master/Slave jumper of the hard disk is located in the middle of the data line interface and power line interface at the end of the hard disk, from 3 ~ Four sets of pins and 1 ~ Composed of two jumpers. There are generally three hard drive jumper setting modes: Master, slave, and cable select. We recommend that you set them to cable select.
Before installing the hard disk, select a hard disk with better performance from the two hard disks as the system boot hard disk and connect it to the end of the 80 pin data cable, connect the other hard disk to the middle of the data line. If both hard disks support ata100/133, we recommend that you directly connect the dual-IDE hard disk to an IDE channel to avoid sharing the channel with the ata33 optical drive. If one of the old hard disks only supports ata66/33, we recommend that you install it with the optical drive in an IDE channel.
Harmony between SATA and IDE Hard Drives
SATA and IDE Hard Disks use completely different interfaces, so it is not difficult to get along with each other. After connecting the data cable to the power interface, you only need to specify the hard disk in the BIOS as the boot disk. In this case, the SATA channel in BIOS is not shared with the IDE channel at all. Generally, an option is directly used to determine which hard disk is used as the boot disk. If you use the scsicard of the PCI interface to install the SATA hard disk, You need to specify the first boot device as SCSI In the bios so that the priority is higher than that of the IDE hard disk. It should be noted that the motherboard of different brands must be set differently, but the general method is as follows.
Solve the Problem of drive character interleaved
If you install a dual hard disk, you cannot leave the drive letter staggered. What is "drive-character staggered? For example. Assume that your first hard disk originally had three partitions: C, D, and E, marked as C1, D1, and E1, and the second hard disk had two partitions: C and D, marked as C2 and D2 respectively. In general, after mounting the dual hard disk, the hard disk partition order will be C-C1, D-C2, E-D1, F-E1, G-D2. In the past, partitions D and E of the first hard disk were changed to disks E and F, and the C partitions of the second hard disk were embedded between disks C and E ". If the drive letter is staggered, the original software cannot work properly due to a path error before the dual hard disk is installed.
In this case, we can take the following two measures to avoid the "drive character staggered ":
Solution 1:
If both hard disks have primary boot partitions, you can set only the first hard disk in bios and the second hard disk to none, in this way, in Windows or Linux, the drive letters will be allocated in sequence based on the IDE interface, so as to avoid the "drive character crossover" and will not damage the hard disk data. In addition, if different operating systems are installed in the primary boot partitions of the two hard disks, You can activate one hard disk by changing the CMOS settings to shield the other hard disk, start different operating systems. The disadvantage is that the hard disk blocked by BIOS cannot be seen in the pure DOS system. However, the NTFS partition era has completely broken with DOS, so this defect is almost negligible.
Solution 2:
Create a primary partition only on the first hard disk (of course there can be other logical partitions), divide all the secondary hard disks into extended partitions, and then divide the logical partitions in the extended partitions, you can completely avoid the "drive character staggered. Of course, back up your data before partitioning the second hard disk. The Windows 2000/XP/2003 operating system comes with the disk manager. Click "start"> "set"> "Control Panel"> "Management Tools"> "Computer Management ", switch to "disk management" and assign a drive letter to each partition. Because the second hard disk is not completely in the primary partition, there is no limit for allocation.
Actual RAID 0
The speed of the hard disk directly affects the efficiency of the entire system, sometimes even more significant than the CPU and memory. Therefore, the RAID 0 disk array working in parallel with the dual hard disk is becoming popular. When reading and writing data, the RAID 0 disk array will be operated at the same time on the two hard disks, this technology can greatly improve the disk performance without losing the total disk capacity.
In the RAID 0 practice of the IDE hard disk, we will use the tekram dc200 chip as an example to introduce it to you. Although it is different from the common promise and highpiont chips, the use method is basically the same, and the use of SATA raid is almost the same. In fact, the key to using RAID 0 is to master the BIOS settings of the raid control card. When we install the raid control card and connect the two hard disks, the following figure will appear when the system starts up.
Select "1. Set RAID configuration" in the menu and press the Enter key to go to the "set RAID configuration" page. The RAID Controller will use a period of time to identify the hard disk. Then, move the cursor to the hard disk, press the Space key to select the disk, and press the Enter key to confirm the selection, A new window is displayed, showing the available raid mode. There are four modes: jbod (not suitable for raid), RAID 0, RAID 1, RAID 0 + 1.
We certainly choose RAID 0 ". Then you can check whether the mode is actually activated through the status menu. Now, the installation of RAID 0 hardware is complete. You can partition and install the operating system. It is worth noting that Windows does not recognize raid control chips, so it recognizes raid controllers as common SCSI control cards. We strongly recommend that you install the correct driver for the RAID Controller after installing windows. This not only improves the stability of the raid system, but also greatly improves the performance. In addition, many raid control cards also provide a wide range of software to help users view the raid status in windows.

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