配置流服务器，第2部分

谢谢你的回忆

Contrary to popular wisdom, adding more memory to a server does not necessarily enhance performance. Look at the performance attributes of the entire server prior to assuming that more memory will speed things up. Also, RAM should be in proportion to the speed of the processor. 处理器越快，它能处理的数据就越多. It’s important to have as much data in memory as the processor can handle.

提示: Real推荐256 MB的RAM来运行它的RealSystem Server. Adding more RAM will increase the number of clients the machine can serve simultaneously. 下表, 由皇马提供, demonstrates how much RAM is needed for various operating environments under measured operations. 你的里程会有所不同. 但这是一个很好的开始.

估计流Served@225Kbs/stream	估计服务带宽	Linux	Windows NT 4.0	Solaris 2.7
高达130	10 MB	奔腾II 350兆赫 512 mb RAM	奔腾III 500兆赫 512mb ram	超10 512mb ram
最多265	30 MB	奔腾III 750兆赫 768 MB ram	奔腾III 750兆赫 768 MB ram	超30 768 MB ram
高达445	60 MB	双奔腾III 750兆赫 1024 MB ram	双奔腾III 750兆赫 1024 MB ram	超60 1024 MB ram
445	100 MB	双奔腾III 750兆赫 1024 MB ram	四奔腾III 750兆赫 2048 MB ram	E250 2048 MB ram

以上内容由皇马提供. RealSystem Server also runs on Windows 2000, HPUX, IBM AIX, Compaq's Tru64, Solaris 2.8和免费BSD.

提示: 为峰值负载配置内存，而不是平均负载. 出于这个原因, 而且因为内存相对便宜, 将上述值加倍是个好主意, 如果可能的话.

提示: Do not allow the server to "swap" to the hard drive when it’s short on system memory. Ensure that there is enough memory so swapping NEVER occurs. Disk drive performance is not even in the same ballpark as memory speed. Swapping (or paging) program instructions and data on and off the hard drive will kill the performance of any system, 尤其是流媒体服务器.

提示: 检查其他变量以获得更多内存. The media server’s ability to maximize available memory may mandate more memory for additional performance. 例如, 在Solaris系统上, RealSystem Server is designed to pre-allocate a large amount of memory and then use memory from that block. This helps ensure smooth streaming and minimize latency from buffering and data fetching.

事实上, many Unix systems are designed to pre-allocate (buffer) large amounts of memory explicitly for media data. Memory buffers can be established for each active video stream, which helps the efficiency of streaming data over the network as the next "cluster" of media data is fetched from the disk. This helps ensure smooth streaming and minimizes latency resulting from disk I/O. This is a good example of how more memory supports more concurrent streams. The ability to buffer multiple concurrent media streams is a function of the media server and its operating system’s ability to maximize available memory.

On the other extreme, Microsoft Media Services does not use system memory to cache file system data. Given the complexity of interaction between server components and the design of Microsoft Media Services, adding more memory may or may not affect the number of concurrent streams the server can run.

来来去去，I/0
Server I/O subsystems are critical to streaming performance yet are the most difficult to configure. The goal is to maintain a sustainable bit rate through the server for multiple concurrent streams. I/O subsystems include the I/O bus, disk bus architecture, host bus adapters (HBAs), and RAID arrays.

I / O总线
There used to be a battle between vendors to introduce new I/O bus architectures, 特性, 和速度. 值得庆幸的是, that war is over and PCI is the winner (but keep your eye on InfiniBand in the near future). Virtually every hardware vendor uses PCI as the standard I/O bus. The advice on this is simple: Get the fastest PCI bus your money can afford.

磁盘总线体系结构
For disk bus architecture, you’ll have two choices: SCSI or IDE/ATA. 对于纯粹的传输速度，您无法击败SCSI. 出于这个原因, SCSI is typically preferred for streaming applications.

下面列出了每种方法的注意事项.

IDE和ATA(IDE/EIDE, Fast-ATA and ATA-2 Ultra-ATA, each is a souped up version of the previous)

磁盘比SCSI便宜

比SCSI驱动器慢多了

更便宜的主机总线适配器

EIDE disk can be configured to emulate SCSI disks within multiple disk arrays, 哪一款性价比更高

轮询I/O意味着处理器完成所有的I/O工作

限制器件(4-EIDE)

Only one IDE drive can transfer between memory and disk at once

较慢的IDE总线传输速率:高达13.3 mb /秒

SCSI

磁盘比IDE/ATA更昂贵

比IDE/ATA驱动器快多了

Host bus adapter prices vary considerably, but still much higher than IDE ($15 IDE vs. 200美元SCSI)

通常基于DMA(释放CPU)

处理更多的设备(15宽SCSI)

SCSI drives operate independently and can all communicate simultaneously on the SCSI bus

SCSI drives are not quite fast enough to flood more than half the SCSI bus bandwidth, so you can have at least two drives on a single bus pumping full speed.

SCSI buses offer the fastest transfer rates: up to 200MB/second; 32 and 64-bit bus (SCSI 3 Ultra 2) - soon to be 512MB/second

提示: You can get near SCSI bus performance (133 mb /秒 and higher) for less cost by going with arrays from companies who have figured out how to create RAID arrays out of IDE drives to make the computer think they are SCSI disk arrays. The IDE/ATA RAID array appears as one large SCSI disk drive to the computer. 看看Medea和Promise这样的公司吧, which specialize in products that spoof the computer into thinking IDE disk drives are SCSI drives (with some limitations) to achieve significantly higher performance.

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