Some programs are written directly on the host computer, running at the bottom level of the operating system. Using the concept of the Big Dipper, they virtualize the physical disks presented by the host's SCSI or IDE controller into various virtual disks, which are then presented to upper-level programming interfaces such as volume management programs. These software programs use a configuration tool to allow users to select which disks to combine and what type of RAID configuration to form.   For example, a machine might have two IDE drives and four SCSI drives installed. The IDE drives are connected directly to the motherboard's integrated IDE interface, while the SCSI drives are connected to a PCI SCSI card. Without the involvement of a RAID program, the system can recognize all six drives, format them with the file system, and mount them to a drive letter or directory for read/write access by applications.   After installing the RAID program, the user uses the configuration interface to configure the two E drives into a RAID 0 system. If each IDE drive originally had a capacity of 80GB, the RAID 0 configuration would create a single "virtual" disk with a capacity of 160GB. The user then configured a RAID 5 system with four SCSI drives. If each SCSI drive originally had a capacity of 73GB, the virtual disk capacity after the four drives were configured in RAID 5 would be approximately the capacity of three drives, or 216GB. Of course, because the RAID program uses some of the disk space to store RAID information, the actual capacity will be reduced. After processing by the RAID program, these six drives are ultimately reduced to two virtual disks. In Windows, opening Disk Manager will only show two hard drives: one with a capacity of 160GB (hard drive 1) and the other with a capacity of 219GB (hard drive 2). These two drives can then be formatted, for example, using the NTFS file system. The formatting program will be completely unaware of the data being written to multiple physical drives.   For example, at a certain moment, the formatting program issues a command to write data from memory start address X to LBA start address 10000 and length 128 on hard drive 1 (a RAID 0 virtual drive composed of two IDE drives). The RAID program intercepts this command and analyzes it. If hard drive 1 is a RAID 0 system, the RAID engine will calculate the data for the 128 sectors starting at LBA 10000, mapping the logical LBAs to the physical LBAs of the physical disks and writing the corresponding data to the physical disks. After writing, the formatter receives a successful write signal and proceeds to the next I0. This process obscures the upper-level program's knowledge of the underlying physical disk details. Other RAID configurations operate in the same way, albeit with more complex algorithms. Even these complex algorithms, when processed by the CPU, are thousands or even tens of thousands of times faster than disk read and write speeds.   STOR Technology Limited provides you with high-quality 9560-16I, 9560-8I, 9361-4I, 9540-8I，9670W-16i, etc. We provide you with higher-quality services and assured after-sales service. Welcome to visit us and discuss related products with us. Our website: https://www.cloudstorserver.com/ Contact us: alice@storservers.com / +86-755-83677183 Whatsapp : +8613824334699  

Understanding server raid cards Raid card: The full name is Redundant Array of Independent Disks Card. It uses Raid technology to turn multiple hard disks into one logical disk, with better capacity, performance, reliability, and manageability SAS card: It is positioned as a low-end hard disk array expansion card. Compared with Raid cards, it has obvious gaps in terms of no cache, Raid level 0, 1, and performance. Onboard raid: refers to the SATA controller integrated in the PCH of the server motherboard, which usually only supports SATA disks, has no cache, poor performance, and has limitations.   The CPU of the RAID card implements the functions of the RAID card by executing the firmware in the flash memory to control the SCSI controller, CacheMemory, and the indication alarm circuit. The operation process is as follows: 1. Initialize the RAID card register 2. Read the last RAID parameters in NVRAM, compare with the actual hard disk information to display the results 3. Send configuration prompts, respond to HOST commands to enter the configuration interface 4. Provide a configuration menu, and store the RAID card parameters and RAID parameters provided by the user in NVRAM 5. According to the RAID parameters, initialize the hard disk write operation through the SCSI controller 6. Complete the configuration and wait for the Host to issue a read and write operation command   STOR Technology Limited provides you with high-quality 9560-16I, 9560-8I, 9361-4I, 9540-8I, etc. We provide you with higher-quality services and assured after-sales service. Welcome to visit us and discuss related products with us. Our website: https://www.cloudstorserver.com/ Contact us: alice@storservers.com / +86-755-83677183 Whatsapp : +8613824334699

For upper-layer write IO, there are two modes for RAID controllers: (1) WriteBack mode: When data arrives from the upper layer, the RAID controller saves it to the cache and immediately notifies the host IO is complete. This allows the host to proceed to the next IO without waiting, while the data remains in the RAID card's cache without being written to the disk. The RAID controller optimizes the disk writes by either writing to the disk individually, in batches, or queuing the IOs using queueing techniques. However, this approach has a critical drawback: if a power outage occurs, the data in the RAID card's cache is lost while the host assumes the IO is completed, resulting in significant inconsistencies between the upper and lower layers. Hence, certain critical applications, such as databases, implement their own consistency detection measures.   Due to this reason, high-end RAID cards require batteries to protect the cache. In the event of a power outage, the battery continues to supply power to the cache, ensuring data integrity. Upon power restoration, the RAID card prioritizes writing the incomplete IOs stored in the cache to the disk.   (2) WriteThrough mode: In this mode, IO from the upper layer is only considered complete after the RAID controller writes the data to the disk. This approach guarantees high reliability. Although the cache's performance advantage is lost in this mode, its buffering function remains effective.   In addition to being a write cache, read cache is also very important. The cache algorithm is a very complex subject, with a set of complex mechanisms. One of the algorithms is called PreFetch, which means that the data on the disk that is "likely" to be accessed by the host next time is "read into the cache" before the host issues a read I0 request. How is this "likely" calculated?   In fact, it is assumed that the host has a high probability of reading the data in the adjacent position of the disk where the data read this time is located in the next IO. This assumption is very applicable to continuous IO sequential reading, such as reading logically continuous stored data. Such applications, such as FTP large file transfer services and video on demand services, are all applications for reading large files. If many fragmented small files are also stored continuously in adjacent positions on the disk, caching will greatly improve performance, because the IOPS required to read small files is very high. If there is no cache, it depends entirely on the head seek to complete each IO, which takes a long time.   STOR Technology Limited provides you with high-quality 9560-16I, 9560-8I, 9361-4I, 9540-8I, etc. We provide you with higher-quality services and assured after-sales service. Welcome to visit us and discuss related products with us. Our website: https://www.cloudstorserver.com/ Contact us: alice@storservers.com / +86-755-83677183 Whatsapp : +8613824334699