Re: Moving partition to an overlapping position

[Andrew Clausen]

On Wed, Jul 20, 2005 at 11:22:21AM +0200, Szakacsits Szabolcs wrote:
> > All Parted operations are theoretically power-loss proof, including
> > resizing supported FS. 
> 
> I'm interested how. I know it's possible but it's not always very trivial.

I wouldn't say it's 100% power-loss proof.  There are small windows
where you can have dataloss, but we kept them small :)  In the ext2
resizer, you're just copying blocks and inodes around, and then
updating the blocks that reference them.  If Parted is interrupted,
e2fsck can fix everything.

The FAT resizer only writes to free space (i.e. copy-on-write), until it
comes to writing the metadata (bootsector, FATs) at the end.

> In the general case ensuring consistency is difficult. Disks and
> controllers can lie that data is on the disk platter but in real they 
> keep it in their cache which can get lost during power outage.

We don't do anything fancy to deal with this.

> Power outage is not a common case

It is for a lot of people.  (Think about all the Indian and Brazillian
users...)

Cheers,
Andrew