Scrub free disk blocks

JD jd1008 at
Sat Aug 28 15:27:14 UTC 2010

  On 08/28/2010 06:22 AM, Patrick O'Callaghan wrote:
> On Fri, 2010-08-27 at 21:53 -0700, JD wrote:
>> On 08/27/2010 09:25 PM, JD wrote:
>>>   Is there a Linux util to scrub free disk blocks and keep everything
>>> else intact ??
>> Someone (not on this list) described a simple way to do this.
>> Scrubbing files to be deleted is easy enough - there are utils for it
>> already.
>> But scrubbing existing free space is slower and requires patience.
>> cd to the root of the partition.
>> sudo dd if=/dev/zero of=ZERO bs=20M
>> When the dd program fails to write any further, you
>> have grabbed and zeroed all available free disk blocks
>> in the partition.
>> Now all you do is use the command scrub to scrub the file ZERO
>> and when done  the file is deleted.
>  From scrub(1):
> -X, --freespace
>                Create  specified  directory and fill it with files until write returns ENOSPC (file system full),
>                then scrub the files as usual.  The size of each file can be set with -s, otherwise it will be the
>                maximum file size creatable given the user’s file size limit or 1g if umlimited.
> However note that neither of these methods guarantees to scrub indirect
> blocks in the filesystem that were used to create the space-filling
> files. Maybe they do, maybe they don't, it's not clear.
> poc
What is not clear from the man page is, when using the -X option, whether or
not the directory and the files created in the directory are automatically
deleted before scrub exits. I will assume that they are. Currently scrubbing
189GB free space.

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