Re: [gentoo-user] 1-Terabyte drives - 4K sector sizes? -> bar performance so far

[J. Roeleveld]

On Wednesday 10 February 2010 08:08:44 Alan McKinnon wrote:
> On Wednesday 10 February 2010 01:22:31 Iain Buchanan wrote:
> > On Tue, 2010-02-09 at 08:47 +0100, J. Roeleveld wrote:
> > > I now only need to figure out the best way to configure LVM over this
> > > to get the best performance from it. Does anyone know of a decent way
> > > of figuring this out?
> > > I got 6 disks in Raid-5.
> >
> > why LVM?  Planning on changing partition size later?  LVM is good for
> > (but not limited to) non-raid setups where you want one partition over a
> > number of disks.
> >
> > If you have RAID 5 however, don't you just get one large disk out of it?
> > In which case you could just create x partitions.  You can always use
> > parted to resize / move them later.
> >
> > IMHO recovery from tiny boot disks is easier without LVM too.
>
> General observation (not saying that Iain is wrong):
>
> You use RAID to get redundancy, data integrity and performance.
>
> You use lvm to get flexibility, ease of maintenance and the ability to
>  create volumes larger than any single disk or array. And do it at a
>  reasonable price.
>
> These two things have nothing to do with each other and must be viewed as
> such. There are places where RAID and lvm seem to overlap, where one might
> think that a feature of one can be used to replace the other. But both
>  really suck in these overlaps and are not very good at them.
>
> Bottom line: don't try and use RAID or LVM to do $STUFF outside their core
> functions. They each do one thing and do it well.
>

I completely agree with this.
RAID is for redundancy (Loose a disk, and the system will keep running)
LVM is for flexibility (Resizing/moving partitions using parted or similar 
takes time during which the whole system is unusable)

With LVM, I can resize a partition while it is actually in use (eg. write-
activities)