Re: Partitioning questions

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On Tue, 2011-01-04 at 12:36 +0800, Gregory Hosler wrote: 
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> On 01/04/2011 02:34 AM, Alex wrote:
> > Hi,
> > 
> > I'm trying to install FC14 x86_64 on a quad-core AMD box with 4 1TB
> > SATA disks, and have some questions about partitioning.
> > 
> > I'd like to create a RAID5 array with no spares, using all four disks.
> > There isn't room in the chassis for more disks, and they will never be
> > replaced with larger ones. Should I even worry about LVM?
> 
> yes.
> 
> raid cannot be partitioned. lvm _is_ partitioning.

That's somewhat misleading, I think.  As I interpret what I do to create
software RAIDs with Fedora:

     1. Partitioning is something that you do to a raw disk. 
     2. Software RAID devices are constructed from partitions on several
        disks.  They behave like partitions, except for the
        replication. 
     3. Partitions or RAID devices can contain filesystems or LVM
        physical volumes. 
     4. Volume groups are collections of physical volumes, which can be
        several independent partitions (either single ones, which could
        appear on several disks or RAID devices). 
     5. Volume groups are sliced up into logical volumes, each of which
        contains a filesystem.

Hardware RAID is a different thing.  Hardware RAIDs are made up of disks
and look like single disks to the OS.  The replication is completely
invisible.

Hope that clarifies things.  If I missed something, I'm sure someone
will correct me.

> 
> so raid5 the 4 disks. put /dev/md0 as the pv into a vg, and then slice it up as
> "partitions" with lvm.

So I suggested RAIDing a set of partitions on each disk as /dev/md0
for /boot (/boot has to be outside of LVM, but it can be RAIDed) and a
set of partitions as /dev/md1 for the LVM.

> 
> as a side benefit you can move the storage from one lv to another lv fairly
> easily (something that is near impossible to do with hard disk partitioning).
> 
> All the best,
> 
> - -Greg
> 
> > If so, do I manually create the RAID5 partitions (and devices) that I
> > want to use, then wrap them in LVM?
> > 
> > By default, the installer creates LVM partitions, but it seems they
> > must be deleted to create the RAID partitions, correct?
> > 
> > The installer is very non-intuitive (and more difficult than it needs
> > to be) if you want to just create RAID partitions and not LVM.
> > 
> > Thanks,
> > Alex
> 
> 
> - -- 
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> Please also check the log file at "/dev/null" for additional information.
>                 (from /var/log/Xorg.setup.log)
> 
> | Greg Hosler                                   ghosler@xxxxxxxxxx    |
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-- 
                Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs
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