Writing zeros to free space in pool

[inedibleoatmeal]

Is it safe to use the cypher /w command in Windows to zeros/random data to the free space in a pool?

[Shane]

If you mean Microsoft's cipher /w, It's safe in the sense that it won't harm a pool. However, it will not zero/random all of the free space in a pool that occupies multiple disks unless you run it on each of those disks directly rather than the pool (as cipher /w operates via writing to a temporary file until the target disk is full, and drivepool will return "full" once that file fills the first disk to which it is being written in the pool).

You might wish to try something like CyLog's FillDisk instead (that writes smaller and smaller files until the target is full), though disclaimer I have not extensively tested FillDisk with DrivePool (and in any case both programs may still leave very small amounts of data on the target).

[Shane]

After some more testing I can confirm cipher /w run on the pool only erases the free space on one drive in the pool before stopping, while filldisk run on the pool appears to leave anywhere from a few megabyes to over a gigabyte untouched on each of the disks in the pool.

Filldisk also reacted similarly when run on individual drives via a mounted path (e.g. E:\Disks\MountedDrive) rather than via a drive letter, which is something to keep in mind if you use the former method to directly access your drives.

Based on observing how DrivePool operated, I would recommend free space cleaning tools only be run directly on the individual drives.

CyLog's Filldisk: Writes only zeroes, so three times faster than cipher /w. Doesn't remove the files it creates after it's aborted or finished, so you can effectively "pause" and you can see for yourself whether the free space is zero afterwards. In testing did not completely wipe the free space on drives accessed via mounted paths. May not scrub deleted files that are very small (1KB) due to how NTFS works.

Microsoft's Cipher: Writes zeroes, then ones, then random bytes so more thorough but three times slower than filldisk. Leaves an empty EFSTMPWP folder on the target afterwards, so hard to check if it gets every last byte and there is a warning in the MS documentation about it potentially missing files of 1KB or less in size. Worked on mounted paths.

SysInternals' SDelete: Like Cipher, but apparently has the 1KB file issue solved.

TRIM: any SSD with TRIM functionality can do this automagically (and thoroughly). A windows command to manually trigger this is defrag volume /o - e.g. "defrag e: /o".

If you are concerned about thieves scrounging through your Windows disks after stealing the machine, I'd recommend Bitlocker and a long passphrase.