On Sat, 10 Jun 2000, David Gould wrote:
> On Fri, Jun 09, 2000 at 12:44:19PM +0100, Stephen C. Tweedie wrote:
> > Hi,
> >
> > On Fri, Jun 09, 2000 at 12:45:51PM +0200, Xuan Baldauf wrote:
> > >
> > > Is it reasonable to use the 50 bytes of /dev/nvram for logging or is it just
> > > too small?
> >
> > Far, far, far, far, far too small. You need tens of kB minimum to record
> > a single filesystem transaction for a complex operation such as a file
> > delete.
>
> Interesting. Or even surprising. I suppose I could just go read the code,
> but for instant gratification of my curiousity, I will ask here first.
>
> What exactly is being logged for a file deletion that takes so much space?
>
> Is this for the general case, or only for files with a lot of indirect
> blocks?
>
It is the same with reiserfs, we log blocks, and each block is 4k.
Deleting a large file (>2GB) could touch thousands of blocks. These can
be broken up into multiple transcations, but even then it could touch 15
or 16 blocks at a time.
But, the other reason you don't want a tiny log is the log limits how long
you can go without flushing the metadata to its real location on disk. If
your log fills in 1 second and you have to start flushing, performance
will suffer badly.
-chris
-
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