From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Brett Russ" Subject: RE: Behavior of tails with respect to shred, wipe, etc Date: Fri, 25 Oct 2002 17:13:03 -0400 Message-ID: References: <15801.26994.705639.374241@laputa.namesys.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com In-Reply-To: <15801.26994.705639.374241@laputa.namesys.com> List-Id: Content-Type: text/plain; charset="us-ascii" To: Reiserfs-List > Tails are stored in leaf nodes of the balanced tree. During balancing > data are copied. When node becomes completely empty it is just dropped > on the floor and disk copy isn't updated. As a result, at any given > moment, some versions of file content can be scattered across different > disk blocks. Moreover, journal area also contains (multiple) copies of > data modified during recent transactions. It sounds like I cannot predict when balancing takes place, i.e. it doesn't always occur as a result of writing the file I am concerned about shredding--it might occur as a result of an unrelated operation. So tails can and will be scattered about and no longer attached to a shreddable inode...hmm. Your comment about the journal containing data--does that apply in my case where I am only journaling metadata? And if so, wouldn't a write/sync flush through the journal and clear that out? > > 2) If someone confirms that there is not a way to guarantee > obliteration of > > original data in all cases with tails, can I assume that > disabling tails > > will rectify the problem? > > I think yes. Reiserfs neither relocates nor journals unformatted blocks > (until data-journalling patches are used). A full block or a partially full block with tail packing disabled is considered an unformatted block? > > 4) What is the best way to determine and read the physical > sectors that a > > file is mapped to in order to verify obliteration? I have used > > debugreiserfs a bit (with the -d option) and get keys and > locations of files > > but the documentation is rather limited on what all of the > output means and > > how to use it. > > > > Look for FIBMAP ioctl. It only works for unformatted blocks. Will check it out, thank you. -Brett