Re: vim file write mode on journaling fs.

[Seth Mos <knuffie@xs4all.nl>]

At 16:26 11-8-2001 -0500, Steve Lord wrote:

>OK, just picking a message to respond to from this thread.

snipping

>   4. Anyone who is shutting down their system by pulling the plug
>      rather than doing an orderly shutdown is asking for trouble.
>      Yes, it is a situation we want to deal with fairly gracefully,
>      but filesystem recovery in journaling filesystems and fsck in
>      others is there to 'recover' from problems, not to cater to
>      lazy users. umount is there for a reason.

Yes, but crashes can ocur in a perfect world.

>     5. With XFS it looks like this:
>
>         o write system call comes in looks for space in the file, if
>           there is none it asks the filesystem for some, the filesystem
>           records the fact that space was requested at this point in the
>           file. A buffer is allocated as before, it is marked dirty, it
>           is also marked delayed allocate. The write returns.
>
>         o Possibly an inode flush or a log flush pushes the new inode
>           out to disk.
>
>         o The bdflush daemon comes along and sees the buffers as being
>           delayed allocate, it calls the filesystem to allocate the space.
>           The allocate is done, and the buffers are written out to disk.
>           The transaction which records the extents is still in memory
>           and will not be flushed for a few seconds yet.
>
>       This last sentence is the major difference, and is probably what is
>       biting here, the write has not really happened until this metadata
>       makes it out to disk. We may be having some issues with how long
>       this is taking in Linux.

Weird, I expected the data to get written first and then the metadata. If 
that would happen you would have no file, or in our case, the old file.

>So the upshot of all of this is that I suspect we do have an issue, and we
>will get to it at some point. In the mean time there is no need to start
>discarding filesystems which do not behave as you want them to do if you
>pull the plug.

Hey, we have lot's of time to fix it. I could have used all those 30 
minutes of time that I saved from fscking my filesystem but I used it to 
play Quake 3 instead.

Cheers

--
Seth
Every program has two purposes one for which
it was written and another for which it wasn't
I use the last kind.