Re: File System conversion -- ideas

[Hans Reiser <reiser@namesys.com>]

Jesse Pollard wrote:

>On Sunday 29 June 2003 14:45, rmoser wrote:
>  
>
>>*********** REPLY SEPARATOR  ***********
>>
>>On 6/29/2003 at 8:42 PM viro@parcelfarce.linux.theplanet.co.uk wrote:
>>    
>>
>>>On Sun, Jun 29, 2003 at 08:28:47PM +0100, Jamie Lokier wrote:
>>>      
>>>
>>>>Consider that many people choose ext3 rather than reiser simply
>>>>because it is easy to convert ext2 to ext3, and hard to convert ext2
>>>>to reiser (and hard to convert back if they don't like it).  I have
>>>>seen this written by many people who choose to use ext3.  Thus proving
>>>>that there is value in in-place filesystem conversion :)
>>>>        
>>>>
>>>Uh-huh.  You want to get in-kernel conversion between ext* and reiserfs?
>>>With recoverable state if aborted?  Get real.
>>>      
>>>
>>no, in-kernel conversion between everything.  You don't think it can be
>>done? It's not that difficult a problem to manage data like that :D
>>    
>>
>
>You are ASSUMING that the new filesystem requires lessthan or equal amount
>of metadata. This is NOT always true. A conversion of a full EXT2 to Riserfs
>would fail simply because there is no free space to expand the needed
>additional overhead.
>
Uh, you mean converting reiserfs to ext2 would fail.... we are more 
space efficient....

>
>Going in the other direction usually is possible (again, depending on the
>filesystem) but there are exceptions... Try converting an EXT2 to DosFS.
>In place. And maintain a recoverable state when aborted.
>
>Not gonna happen.
>
>Too much depends on what the target filesystem is, and what it may require.
>
>Consider another - switching to an extent filesystem... If the datablocks 
>don't move, then you need MORE extents than the current indirect pointers.
>And each extent is LARGER than the indirect pointers.
>
>Then you have to compress/condense the extents (requiring shuffling data
>blocks around to reduce the number of extents). Each requires free space
>to do it's work, and the amount of free blocks is not the same.
>
>Faster to do a copy. more reliable too. and recoverable.
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>  
>


-- 
Hans