Re: Can Debian Backup ntfs File System?
On Sun, 28 Nov 2010 18:48:18 +0100, Axel Freyn wrote:
> Hi Camaleón,
>> > But that is extremly dangerous...: you risk to loose/destroy
>> > informations on the damaged filesystem (nobody guarantees, that
>> > scandisk is not destroying data...). And especially defrag: this WILL
>> > destroy data, which are in lost files (=sectors of the harddisk which
>> > seem to be free according to the file system...).
>>
>> (...)
>>
>> I've never heard neither seen that before and have worked with ntfs
>> volumes during many years. In fact, I've managed to "restore to live"
>> windows systems that were unable to boot up by following that procedure
>> (even an unexpected shutdown can make the OS to be unbootable -system
>> files tend to become easily corrupted- and checking the file system
>> structure solves the issue).
>>
>> Scan disk (chkdsk) and defrag are the standard and recommended tools
>> for dealing with MS file systems problems. Maybe they cannot solve the
>> problem but won't aggravate it either. And before "wiping out" the hard
>> disk, I think it is at least worth a try.
> The point I wanted to make is the following: Defrag shifts parts of the
> files -- and in order to do so, it OVERWRITES unused parts of the disk.
> Now: as soon as the filesystem is corrupted, one can't trust anymore in
> the information which parts are "unused" -- so it can happen that defrag
> (or any other tool which writs on the disk) overwrites
> file-informations, which belong to a "lost" file, but which are believed
> to be "free" and "unused" by the filesystem. In my opinion, this danger
> is not limited to ntfs, but exists in every filesystem: as soon as the
> filesystem is corrupted, one can't guarantee that the blocks marked as
> "free" don't contain usefull information -- and that's why I wouldn't
> write anything on the partition!
>
> A similiar point is true for scandisk / chkdsk: Again, independent on
> the filesystem: Once the filesystem is corrupted, the recovery tool has
> to make assumptions about what is the "correct" information -- and if it
> makes the wrong assumption, it WILL destroy data. For example: How can
> chkdsk guarantee that, whenever it writes some information on the disk,
> it uses a truely "free" part of the disc? maybe on this place was a
> piece of an important file, which was lost by the file-system
> corruption?
Well, no need to worry. You are thinking in the worst scenario but even
if the file system structure is completey destroyed, "defrag" is also
capable of performing a test only disk analysis and so does "chkdsk".
> Of course the question is, how important the data are -- is it worth the
> effort to first create a copy of the partition and then to work on the
> copy?
A backup copy is always desiderable. In fact, there should already exist
a copy with the latest backup... of a "week" ago and not from a "year"
ago >:-)
Greetings,
--
Camaleón
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