Hardware Reference
In-Depth Information
written to the drive, and it might even corrupt the entire file system. This is where the journaling in
NT File System (NTFS) comes in handy, which is one of the main reasons NTFS is recommended
over file allocation table (FAT).
Note
If a power outage occurs while you are writing a file to a storage device using a FAT file
system, in addition to losing the file, you'll likely end up with lost clusters, cross-linked files,
or other file system damage, potentially causing a much greater loss of data than just the one
file being written at the time. However, if the same outage occurs while writing to a device
using NTFS, the file system itself won't be damaged. Of course, no matter what file system is
used, you will almost certainly lose part or all of the file being saved at the time of the outage
because even if you have write caching turned off, you can't recover data that never made it to
the disk in the first place.
In addition to the Windows cache, there is the drive's built-in physical write cache, which is also
enabled by default on internal drives. Depending on the specific hardware and drivers involved, this
functionality might also be overridden or controlled by Windows. If it can be controlled, the Policies
tab in the drive properties under the Device Manager has a setting called Enable Write Caching on
the Disk, which allows Windows to turn the drive's hardware write caching function on or off. Note
that the dialog box for Enable Write Caching on the Disk states the following:
This setting enables write caching to improve disk performance, but a power outage or equipment
failure might result in data loss or corruption.
In my opinion, this statement is more of a disclaimer than a serious warning of danger. The truth is
that when you're saving a file during a power outage, the difference in data loss between whether you
had the drive's internal write caching on or off will be virtually inconsequential. However, I would
say that if your system is experiencing frequent crashes or power outages under normal operation,
disabling the drive's internal write caching (and Windows lazy write caching for external devices as
well) via the settings in the Device Manager
might
result in less data loss in some circumstances.
With removable devices, you can change Windows lazy write functionality via the Optimize for
Quick Removal (lazy write off) or Optimize for Performance (lazy write on) settings in the Policies
tab under the drive properties in the Device Manager entry for any removable devices (that is,
USB/FireWire drives). In addition, optimizing for quick removal automatically turns off the drive's
internal cache.
Figure 14.18
shows the default setting for external USB drives.
