[linux-lvm] Keeping swap in the middle of the disk

[Jos Visser]

And thus it came to pass that Chris Wilson wrote:
(on Fri, Jan 26, 2001 at 07:57:13PM +0000 to be exact)

> On Fri, 26 Jan 2001, Jos Visser wrote:
> 
> > Hi Chris,
> > 
> > The setup you describe will work. Use pvcreate to make hda2, hda4, hdc2
> > and hdc2 into physical volumes, and group them into one volume group
> > (using vgcreate/vgextend as appropriate). Then create one big logical
> > volume in that vg. 
> 
> If I do this then surely it either ends up striping across all four
> partitions (so each disk would be continually seeking from one partition
> to another) or not do any striping at all?

When you put multiple PV's in a VG, it does not stripe, but it
concatenates. Depending on the locality characteristics of the file
system you are using, processing a single file usually hits one PV only,
*unless* you explicitly stripe the LV, in which case it indeed *does*
stripe across all four PV's. The setup you describe which first combines
two partitions into a concatenated metadevice, and then combine these
two as PV's in a VG would be the better approach.

On the other hand, why not create two gigantic 46GB PV's, and create
swap logical volumes as well as a ReiserFS lvol?

++Jos

> 
> > However, I must say that placing the swap area's in the middle of the
> > disk strikes me as somewhat overkill. I dare venture that this is almost
> 
> I guess so... it looks like I'm gonna end up with it at one end of the
> disk.
> 
> > never necessary nowadays. Theoretically you are right, but the
> > things modern disk drives and operating systems do to minimise disk
> > I/O's make it kinda hard to predict what will be going on anyways.
> > Optimising swapping is optimising at the wrong level of the storage
> > hierarchy anyway. And, on another note, it might be more worthwhile to
> > make sure the ReiserFS journal is in the middle of the disk, since that
> > is most definitely a hot spot in the file system.
> > 
> > ++Jos
> > 
> 
> Cheers,
> 
> Chris
> 
> -- 
> jakdaw at xmms.org

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