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

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On Thu, Feb 27, 2014 at 09:16:10PM +0000, Dafna Ron wrote:

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.

To be more precise: if not using "Wipe on delete" on block storage, the same storage used by the deleted disks is to be used for a future vDisk. If that disk is to be allocated as raw storage, and it is attached to another VM, that VM would have access to the original data. If you trust your VMs, or use qcow, or mkfs before running guests, you do not need this io-eating flag. Dan.