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

For parity RAID, after the RAID parameters are set on the RAID card and the RAID Settings are applied, all the disks in the RAID array need to be initialized. The time required is related to the number and size of the disks. The larger the disk, the more there are, and the longer it will take. Consider: What does a RAID card write to disk? You can think about a new disk just out of the factory, is there any data on it? Yes. What data? It's either all zeros or all ones. Here, all zeros refer to the actual data part, except for some special positions such as sector headers. Because the magnetic region on the disk has two states, either the n-pole or the S-pole. So that means it's either 0 or 1, and there can't be a third state. So what about these 0's or 1's? Of course, these magnetic regions don't have a chaotic state between 0 and 1. If we do RAID5 with a few disks, but do not change any data on the disks, let's see what state we will be in at this point, say 5 disks, 4 data disk space, 1 parity disk space, on the same strip, 4 data blocks, 1 parity block, and all the data on the blocks are all 0, then if we calculate RAID5, It's true, because 0 XOR 0 XOR 0 XOR 0 XOR 0 XOR 0=0, right. If you start with all 1's, then similarly 1 XOR 1 XOR 1 XOR 1 XOR 1 XOR 1=1, also true. However, if RAID5 is made of 6 disks, and the initial values are all 1, the situation is contradictory. 1 XOR 1 XOR 1 XOR 1 XOR 1 XOR 1 XOR 1 =0, in which case the correct result would be that the parity block is 0, but the initial disk is all 1, and the parity block data is also 1, which contradicts the calculation. If the initialization process doesn't make any changes to disk and we just write data, for example, we write a piece of data to the second extend, changing 1 to 0, and then the controller validates the data according to the formula: parity data for new data = (old data EOR new data) EOR. (1EOR 0) EOR1=0, and the new parity is 0, so the final data looks like this: 1 XOR 0 XOR 1 XOR 1 XOR 1 XOR 1. We figured it out to be equal to 1, but the RAID controller figured it out to be 0, so there's a contradiction. Why did you make this mistake? That's because the RAID controller didn't start with a proper data relationship in the first place, and the parity data of the parity block was inconsistent with the data block at the beginning, which led to more and more errors. So after the RAID controller is set up and enabled, in the process of initialization, it needs to write 0 or 1 for each sector of the disk, and then calculate the correct parity bit, or do not change the data of the data block, directly use these existing data, recalc the parity block data of all strips. On this basis, new incoming data will not be misrepresented. Tip: For products such as NetApp, RAID groups do not need to be initialized and are available immediately. Even adding disks to a RAID group that already has data does not cause any additional IO. Because it will reset all Spare disks, that is, send a Zero Unit SCSI instruction to the disk, and the disk will automatically perform the zero. For RAID groups made from these disks, there is no validation and therefore no initialization, or waiting for the disks to clear to zero.   Unleash the power of data! Classic reliability, innovative evolution - RAID Card brings you beyond imagination performance and reliability. Whether you are an individual user, an enterprise, or a data center, our RAID cards will provide you with unparalleled data protection and high-speed transfer. STOR Technology Limited provides original and new cloud storage products, such as megaraid sas 9341 8i, lsi 9361 8i 2gb, lsi megaraid 9460 8i, etc., welcome to consult.

LSI 9440-8i is a RAID controller with the following specifications and advantages:   Specification: 1. Interface: The LSI 9440-8i is equipped with eight internal SATA/SAS ports to support the connection of multiple hard drives and mass storage devices.   2.RAID support: The controller supports multiple RAID levels, including RAID 0, RAID 1, RAID 5, RAID 6, RAID 10, and RAID 50, as well as JBOD (Independent Disk Only) mode. This provides flexible data protection and storage configuration options.   3. Data transfer rate: The megaraid 9440 8i supports SAS data transfer rates up to 12Gb/s, providing fast and stable data transfer.   4. Cache and Processor: The controller is equipped with 2GB DDRIII cache and built-in I/O processor for fast RAID computations and data operations to improve system performance.   5. Backup Battery Module (BBU) support: megaraid sas 9440 8i supports the insertion of a backup battery module to provide the protection of cached data and power failure recovery.   Advantages: 1. High performance and reliability: LSI 9440 8i provides high-speed data transmission and processing capabilities, suitable for application scenarios that require large capacity storage and high performance. The supported RAID level and cache mechanism can provide data redundancy and fault tolerance, and ensure data security and reliability.   2. Data protection and Redundancy: With different RAID levels, LSI 9440-8i allows to configure redundancy and data mirroring to provide fault tolerance and data redundancy to ensure that data is not lost.   3. Flexible storage configuration: Supports a variety of different RAID levels and JBOD modes, enabling users to flexibly configure storage according to their specific needs.   4. Management and monitoring: LSI 9440-8i（05-50008-02）provides management tools and monitoring functions for configuring controllers, monitoring disk status, troubleshoing and performance optimization to improve the efficiency of system management and maintenance.   High performance LSI 9440 8i, professional after-sales service, new original quality assurance, three-year warranty, immediately enjoy the factory price!