The way to improve server performance is to find the bottleneck that restricts server performance. Different applications may have different bottlenecks, some should focus on the processor and memory, and some should focus on the I/O throughput of hard disk or network; So, in which application environments should we focus on the server hard disk bottleneck?
Messaging/E-mail/VOD: fast I/O is the key to this kind of application, and the I/O throughput of hard disk is the main bottleneck;
Data warehouse (online transaction processing/data mining): large-scale commercial data storage, cataloging, indexing, data analysis, high-speed commercial computing, etc. , need to have good network and hard disk I/O throughput;
Database (ERP/OLTP, etc. ): To run the database, the server needs strong CPU processing power, large memory capacity to cache data and good I/O throughput performance;
Other applications: the application focuses on data query and network communication, and the hard disk needs to be read and written frequently, so the performance of the hard disk will directly affect the overall performance of the server.
Factors affecting hard disk
When it comes to the index parameters of the hard disk, we should first mention the interface standard of the hard disk. At present, there are two main hard disk interfaces: EIDE and SCSI. Of course, there are also IEEE 1394 interface, USB interface and FC-Al interface products, but they are rare. At present, almost all microcomputers generally adopt hard disks with IDE interface based on Ultra DMA/33/66/ 100 standard, which has the advantages of low price and high popularity.
At the same time, some low-end servers have adopted IDE hard disks. At present, almost all server motherboards are integrated with IDE controllers, but they are generally only used to connect low-speed peripheral IDE CD-ROMs of middle and high-end servers, and SCSI interface standards are generally adopted for hard disks. For example, Inspur Xin Ying servers generally use Ultra 160 SCSI hard disks to provide higher hard disk throughput. SCSI interface hard disk has the advantages of extremely low CPU occupancy, many supporting devices and obvious working advantages under multi-task, which is more suitable for the needs of server applications. Of course, the price of SCSI hard disk is much higher.
However, the bottleneck of hard disk data transmission system is not the speed of PCI bus or interface, but the hard disk itself, which is caused by many factors such as the mechanical part and structural design of the hard disk.
Indicator for measuring hard disk
Indicators to measure hard disk performance mainly include:
Spindle speed
Among all the indexes of hard disk except capacity, spindle speed is the most noticeable performance parameter, and it is also the first decisive factor to determine the internal transmission speed and continuous transmission speed of hard disk. At present, the speed of hard disk is mostly 5400 rpm, 7200 rpm, 10000 rpm, 15000 rpm. Judging from the current situation, SCSI hard disk with 10000rpm has the advantage of high cost performance and is the mainstream of hard disk at present, while hard disks with 7200rpm and below are gradually fading out of the hard disk market.
Internal transmission rate
The internal transmission rate is the decisive factor to evaluate the overall performance of hard disk. Hard disk data transfer rate is divided into internal transfer rate and external transfer rate; Usually, the external transmission rate is also called Burstdata transmission rate or interface transmission rate, which refers to the speed of outputting data from the hard disk cache. At present, the external transmission rate using Ultra 160 SCSI technology has reached160 MB/s; The internal transfer rate, also known as the maximum or minimum continuous transfer rate, refers to the speed at which the hard disk reads and writes data on the disk. At present, most mainstream hard disks are between 30MB/s and 60 MB/s. Because the internal transmission rate of hard disks is less than the external transmission rate, only the internal transmission rate can be used as a real standard to measure the performance of hard disks.
The amount of storage per disk
In addition to the contribution to capacity growth, unit disk storage has another important significance in improving the data transmission speed of hard disk. The increase of storage capacity per disk benefits from the increase of track number and linear magnetic density in tracks. The increase in the number of tracks is of great benefit to reducing the seek time of the magnetic head, because the radius of the magnetic sheet is fixed, and the increase in the number of tracks means that the distance between tracks is shortened, and the positioning time required for the magnetic head to transfer from one track to another is shortened. This will help to improve the speed of random data transmission. The increase of linear magnetic density in the track is directly related to the continuous data transmission speed of the hard disk. With the increase of track linear density, more data can be stored in each track, so that more data can be read from the head to the buffer of the hard disk in each circular motion of the disk.
average seek time
Average seek time refers to the time required for the head to move to the track where the data is located, which is an important index to measure the mechanical performance of the hard disk. Generally, it is between 3 ms and13 ms. It is recommended not to consider SCSI hard disks with a average seek time greater than 8 ms.. Average seek time and average waiting time (completely determined by the rotation speed) jointly determine the time for the hard disk head to find the cluster where the data is located. This time directly affects the random data transmission speed of the hard disk.
stash
Improving the capacity of hard disk cache is also a shortcut to improve the overall performance of hard disk. Because the internal data transmission speed of the hard disk is different from the external data transmission speed. Therefore, cache is needed to make speed adapters. The size of the cache has a great influence on the continuous data transmission speed of the hard disk. Its capacity is 5 12KB, 2MB, 4MB or even 8MB, 16MB. For video shooting, image editing and other work that requires a lot of disk input/output, large-capacity hard disk cache is an ideal choice.
Knowing the performance index of the server hard disk, the next step is to choose the server hard disk suitable for specific applications to improve the working performance of the system.
Choose a high-performance hard disk.
Because SCSI has the advantages of low CPU occupancy, high efficiency of multi-task concurrent operation, many connected devices and long connection distance, it is recommended to use SCSI hard disk and the latest Ultra 160 SCSI controller for most server applications. For low-end small server applications, you can use the latest IDE hard disk and controller. After determining the interface and type of hard disk, we should focus on the technical indicators that affect the performance of hard disk mentioned above, and choose the most cost-effective hard disk scheme according to the factors such as speed, single disk storage, average seek time and cache, combined with the capital budget.
RAID technology
Redundant disk array RAID system provides higher performance index, data integrity and data availability than ordinary disk storage, especially in the increasingly prominent bottleneck problem that hard disk I/O always lags behind CPU performance. RAID solution can effectively make up for this gap.
According to the different verification methods of disk array data, RAID technology is divided into different levels, and each level has different technical characteristics. Readers can refer to the relevant manuals for selection.
In order to better improve the I/O performance of hard disk, RAID technology is recommended. According to the characteristics of the application, the hard disks that are frequently accessed and read are made into RAID0 or RAID 1 or RAID5. At present, IDE RAID can be used in low-end servers, such as Inspur Xin Ying NP200 high-end servers. It is recommended to adopt SCSI RAID controller, and pay attention to the relevant technical indicators of RAID controller, such as CPU type, channel type and number, cache number, battery backup, etc. It should be noted that the RAID controller integrated on the motherboard takes up the SCSI hard disk controller on the motherboard because there is no hard disk controller, which will consume more main processor time and affect the processing capacity of the server.
Hot plug technology
In addition to evaluating the hard disk from the performance index, the failure rate, average trouble-free operation and maintainability of the hard disk should also be considered. In specific applications, priority should be given to hard disks with long service life and low failure rate, which can reduce the probability and frequency of failures, which involves MTBF (Mean Time Between Failures) and data protection technology of hard disks. The larger the MTBF value, the better. For example, the MTBF value of the hard disk used by Inspur Xin Ying server generally exceeds 654.38+200,000 hours. S.M.A.R.T (self-monitoring, analysis and reporting technology) and similar technologies, such as DST (drive self-test) and DFT (drive health test) of Seagate and IBM, are of great significance to the security of data stored in hard disks.
In addition, once the hard disk is damaged, we should consider how to ensure that data is not lost and reduce the downtime of the server. RAID technology can be used to ensure the reliability and security of data, and hot plug technology of hard disk can ensure that the server can still run normally while replacing or repairing hard disk. At present, hot plug technology is very common in middle and high-end servers, and it has always been regarded as an important symbol of server grade. Usually, the components used by hot plug technology in the server include hard disk, power supply, fan, PCI slot and so on. , SCSI hard disk and SCA2 interface (80 pins) specially supporting hot plug technology can be used together with SCSI backplane.