Re: ReiserFS vs XFS or JFS?

["markw-4" <user=5@nabble.blu.org>]

 > If the raw file containing your database is represented inside the 
> structures used by a filesystem and something in the filesystem gets 
> trashed, having a journaled database isn't going to help at all because 
> the journaling information will be inaccessible, since it's also stored 
> in the trashed filesystem. 

Depending on the database that may be true, but a block level journaling 
database like Oracle or PostgreSQL that is likely not true. I know 
PostgreSQL better, so I explain using it as an example. 

Assuming an active database, one is which there may  be re-usable space in 
existing blocks and PostgreSQL WAL files are fairly constant in size. 

Assume that the file system will not be obliterated on a power failure. 
That it is robust enough (or simple enough) to merely have lost chains. I 
would use something like DOS FAT as a model. Simple to the point of being 
stupid. 

When a database table grows, it grows in fixed sized blocks (like FAT). 
After each database write, fsync is called. Far more often than not, only 
the data within a file changes while the disk allocation and file system 
information remain constant. 

The meta information and file system never needs to be journaled because 
the file's "file system" characteristics change relatively infrequently 
and when they do, fsync will be called immediately. There will never be 
any real benefit from the file system journal and you'll end up doing the 
same work twice. 


> 
> So, if you store your database inside a filesystem, double journaling is 
> unavoidable if you want your data safe.  The preferable alternative is 
> to avoid the structures involved in a filesystem, and allocate an entire 
> partition to your database.  Then all you have to worry about is if the 
> partition table were to get trashed, so make a backup of block 0 of the 
> disk. 
> 
>     Mark R. 
> 
> [hidden email] wrote: 
>> IMHO: 
>> EXT2 is great for a database journal in that you won't be double 
>> journalling. (I often speculate that a very minimal UNIX file system 
>> designed for purely for speed and regularly sized blocks, something like 
>> a 
>> streamlined FAT system, would be awesome for databases.) 
>