"Stephen C. Tweedie" wrote:
>
> Hi,
>
> On Tue, Jun 06, 2000 at 09:17:33AM -0700, Chris Mason wrote:
> >
> > The dedicated log device is really important, and I do have bytes reserved
> > to make both that and the multiple filesystems to a single journal work.
> >
> > Once the dedicated log device is coded, I would rather see the shared
> > journal disk idea done through LVM than in the journal code. LVM already
> > has all the tools to find the hot spots on the disk, allowing the admin to
> > move the i/o hogs to different disks. Mostly, I would prefer not to deal
> > with the added complexity in the FS code unless people can find a huge
> > list of reasons it would be better than using lvm.
>
> It really does need to be done in the journal layer, for one simple
> reason --- performance. You need to make sure that the journal
> device is streaming to disk sequentially as much as possible, and that
> means that, ideally, you want to be able to interleave blocks from
> different filesystems into the same journal disk.
>
> A minimal journal management API to allow that should be fairly simple
> to achieve, but because of the write ordering requirements, I don't
> think we could do this through the existing LVM code.
>
> Cheers,
> Stephen
In the 2.5 timeframe I'd like to eliminate the need for a journaling device by
distributing it over the FS using wandering logs.
In the 2.4 timeframe separate log devices are fine.
Hans
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