[Users] The purpose of "Wipe on delete" ?

[Sandro Bonazzola]

Il 27/02/2014 22:16, Dafna Ron ha scritto:
> wipe = writing zero's on the space allocated to that disk to make sure any data once written will be deleted permanently.
> 
> so it's  a security vs speed decision on using this option - since we zeroing the disk to make sure any information once written will be overwritten,
> a delete of a large disk can take a while.

I think this may be not really useful, zeroing files on modern file systems can't grant any kind of security improvement.
According to shred man page:

       CAUTION: Note that shred relies on a very important assumption: that the file system overwrites data in place.  This is the traditional way to
do things, but many modern file system designs  do  not
       satisfy this assumption.  The following are examples of file systems on which shred is not effective, or is not guaranteed to be effective in
all file system modes:

       * log-structured or journaled file systems, such as those supplied with AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)

       * file systems that write redundant data and carry on even if some writes fail, such as RAID-based file systems

       * file systems that make snapshots, such as Network Appliance's NFS server

       * file systems that cache in temporary locations, such as NFS version 3 clients

       * compressed file systems

       In the case of ext3 file systems, the above disclaimer applies (and shred is thus of limited effectiveness) only in data=journal mode, which
journals file data in addition to just metadata.  In both
       the data=ordered (default) and data=writeback modes, shred works as usual.  Ext3 journaling modes can be changed by adding the data=something
option to the mount options for a particular file system
       in the /etc/fstab file, as documented in the mount man page (man mount).

       In addition, file system backups and remote mirrors may contain copies of the file that cannot be removed, and that will allow a shredded file
to be recovered later.



> 
> Dafna
> 
> 
> 
> 
> On 02/27/2014 04:14 PM, Richard Davis wrote:
>> Hi
>>
>> What is the purpose of the "Wipe on delete" option for a VM disk ?
>> Why would you not want data wiped on delete if the alternative is to leave LV metadata and other data languishing on the SD ?
>>
>>
>> Thanks
>>
>> Rich
>> _______________________________________________
>> Users mailing list
>> Users at ovirt.org
>> http://lists.ovirt.org/mailman/listinfo/users
> 
> 


-- 
Sandro Bonazzola
Better technology. Faster innovation. Powered by community collaboration.
See how it works at redhat.com