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    2011年11月17日 12:25


  • 看看当前Write-caching settings是怎样的?


    Write-caching settings


    “Write caching” in a storage device refers to the use of high-speed volatile memory to collect write commands sent to data storage devices and cache them until the slower storage media (either physical disks or low-cost flash memory) can accommodate them. Most devices that use write caching require that power be supplied continuously.

    Quick removal

    This option is usually the best choice for devices that you are likely to remove from the system frequently, such as USB flash drives, SD, MMC, Compact Flash, or similar memory cards, and other externally attached storage.

    When you select the Quick Removal option, Windows manages commands sent to the device using a method called write-through caching. In write-through caching, the device operates on write commands as if there were no cache. The cache may still provide a small performance benefit, but the emphasis is on treating the data as safely as possible by getting the commands to the principal storage. The main benefit is that you can remove the storage device from the system quickly without risking data loss. For example, if a flash drive were to be accidentally pulled out of its port, the data being written to it is much less likely to be lost.

    Better performance

    This option is usually the best choice for devices that must provide the highest possible performance and that you intend to remove from the system infrequently. If you choose this option and the device is disconnected from the system before all of the data is written to it (such as if you remove a USB flash drive), you could lose data.

    When you select the Better Performance option, Windows uses a method known as write-back caching. In this method, the storage device itself is allowed to determine whether using the high-speed cache will save time completing the write commands. If it will, the device signals to the computer that the data has been stored successfully even though the data may not actually be present in the principal storage (such as the disk or flash memory). This method markedly increases the throughput of storage operations, which are often a major bottleneck for system performance overall. However, if the power supplied to the device fails for any reason, any data still in the cache (that the computer system believes is safely stored) could be lost.

    Cache flushing

    By default, Windows employs cache flushing. This means that the system will periodically instruct the storage device to transfer all data waiting in the cache to the principal storage media. When you select Enable write caching on this device, you turn off these periodic commands to transfer the data. Not all devices support all of these features.

    If high data transfer performance is your paramount concern, you should enable both settings: in the Removal Policy section, select the Better Performance option and in the Write-caching policy section, select Enable write caching on the device (if the system hardware and storage device support these features).

    How can I change the write-caching setting for this device?

    Most consumer-oriented storage devices such as USB flash drives, SD or MMC memory cards, or consumer external disk drives do not allow you to change the device’s caching settings. Internal SATA or serial-attached SCSI hard drives shipped with Windows do typically allow you to change the settings, although this can only be guaranteed by the manufacturer of the device. To understand the caching features offered by a given device and determine which settings best suit your needs, consult the documentation provided by the manufacturer.

    More information on preventing data loss

    Systems that have write-caching enabled at any point in path between the application and the storage device must be stable and not prone to power loss. When a device attached to a system uses write-caching, the device’s algorithms for caching are designed with the expectation that power will continuously be available to operate both the cache and the movement of the data in and out of the cache. If your system or power source has known issues with sustaining power, you should not use these features.

    You should also remove storage devices like USB flash drives, SD, MMC, or Compact Flash memory cards, and external storage drives cautiously. When you use the Safe Removal option, your data is protected by Windows in most scenarios. However, it is possible that certain drivers or applications may not conform to the Windows model, and this could lead to data loss when you remove such devices. Whenever possible, it is best to use the Safe Removal applet before you remove any external storage device from the system.
    2011年11月24日 1:17