lost+found

[Jerlique Bahn]

Hello Chuck,

> Jerlique Bahn wrote:
> > If I pull the power on my server whilst its doing heavy IO, should I get
> > files in lost+found if my raid card has battery backed cache?
> 
> Yes, it's still possible.
>
> The cache on the RAID card will be flushed OK, but any in-process
> operations by live processes will be interrupted in the middle if the OS 
> goes away. While some operations are atomic (things like unlink or move),
> simply writing pieces out is not...

Ok, this is contrary to what was my belief, but I guess it really does makes
sense. Eg Suppose we are talking about writing a 1gb file. This obviously
needs to be written to the disk, and not stored in cache. 

So can you explain the process of ufs writing the file, and what ends up in
lost+found if the server is rebooted part way through eg say we are 3/4 of
the way through writing the file before reboot.

Or better still are there any "semi-technical" white papers/web-pages which
could explain this, and under what circumstances lost+found is used.

> > I would like to also know how to turn off (or check) caching on the
> physical
> > disk itself.
>
> smartmontools port?  sysctl hw.ata.wc...?

Sorry I should have mentioned I'm using SCSI disks behind a raid card ;)
 
Thanks for your comments!

JB