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Windows has a setting to turn off the write-cache buffer (see image)

Turn off Windows write-cache buffer flushing on the device
To prevent data loss, do not select this check box unless the device has a separate power supply that allows the device to flush its buffer in case of power failure.

Is it feasible and economical to get such a "separate power supply" for the internal sata drives of a non-server PC? Under what name is such a power supply sold?

I know that there are UPS devices that can be connected to external drives,but what is required to be able to switch this setting safely on for an internal disk?

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The setting has different descriptions in different version of windows

  • Windows XP:
    Enable write caching on the disk
    This setting enables write caching in Windows to improve disk performance, but a power outage or equipment failure might result in data loss or corruption.

  • Windows Server 2003:
    Enable write caching on the disk
    Recommended only for disks with a backup power supply. This setting further improves disk performance, but it also increases the risk of data loss if the disk loses power.

  • Windows Vista:
    Enable advanced performance
    Recommended only for disks with a backup power supply. This setting further improves disk performance, but it also increases the risk of data loss if the disk loses power.

  • Windows 7 and 8:
    Turn off Windows write-cache buffer flushing on the device
    To prevent data loss, do not select this check box unless the device has a separate power supply that allows the device to flush its buffer in case of power failure.

This article by Raymond Chen has some more detailed information about what the setting does.

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2 Answers 2

I rather doubt that they mean a USB hard drive (which can have a seperate power supply on 3.5 inch drive based models) - since you risk data loss as data is transmitted to the system over USB, so I believe they mean san or nas style storage, possibly exposed over ISCSI or ESATA (the latter sounds like the most plausible option). I do also note with a dummy load/jumper on the 20/24 pin connector you could power a hard drive off a seperate PC style PSU .

In short, you can, it would just likely be a seperate computer or dedicated storage device unless you used an unusual, unsupported and frankly odd setup. With any other scenario, test it before you do it. Or better yet, don't switch on that setting, then unplug power from a drive.

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A UPS (Uninteruptable Power Supply) is a "power supply", it is seperate. If a good quality UPS is used for the whole computer it would maintain power during a power failure so a write cache flush could be completed to an internal drive. On a power failure A user would then shut down the computer, before the battery Ran out in the UPS, or an automated procedure would shut down the system using the windows UPS service (or other software).

Shutting down or rebooting the windows system properly will force a write cache flush.
If the battery power ran out on the UPS while writes were still occuring, it could still be a problem. Generally with all the things going on (writing) in a windows system, either the person will be present (to shut down), or they will have an automated shut-down, to be fully safe in a power failure. If the power failure was short, a UPS could maintain operation until the power returned, and flushing would occur normally.

There exists a few specialised battery backups "internal" for computers , like on high end raid cards, so the raid cards can finish , But there is nothing special required internally beyond a good UPS device to maintain the power for the whole computer.

I use a UPS and have tested that switch being on, and have not lost or corrupted data during a few power outages. Although In my uses of the computer I have not observed any benefit at all from delayed flushing.

A UPS could maintain the power for an external drive plugged into the UPS properly, and for the internal drives when the whole computer is battery backed up with a good UPS.

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