Hardware Reference
In-Depth Information
straight to the disk. The truth is, to minimize the potential for lost data, lazy write (Win-
dows write caching) is disabled for
removable
media in Windows by default. This was
designed tominimize problems stemming fromwhatMicrosoft calls the
surprise removal
of certain hardware. Lazy write is enabled by default for internal (ATA or SATA) stor-
age devices inside the computer that cannot be surprise removed. Lazy write is also en-
abled for certain high-performance external storage devices that might or might not be
hot-swappable, such as those attached via eSATA or SCSI.
Many people worry about write caching as related to potential data loss. A worst-case
scenario is a power outage while saving a file, which will certainly cause the loss of data
that hasn't already been written to the drive, and it might even corrupt the entire file sys-
tem.ThisiswherethejournalinginNTFileSystem(NTFS)comesinhandy,whichisone
of the main reasons NTFS is recommended over file allocation table (FAT).
Note
Ifapoweroutage occurswhile youarewriting afile toastorage device usingaFATfile sys-
tem, 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.
Inmyopinion,thisstatementismoreofadisclaimerthanaseriouswarningofdanger.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 in-
consequential. However, I would say that if your system is experiencing frequent crashes
orpoweroutagesundernormaloperation,disablingthedrive'sinternalwritecaching(and
