Re: Partitioning questions

On Tue, 2011-01-04 at 22:09 -0500, Alex wrote:
Hi,

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.

Or a RAID array when setting up LVM on top of it, correct?

I don't think so. For Anaconda (the installer), a software RAID device
is a collection of partitions, one per disk. You can't create the RAID
device unless you already have partitions on the disks designated as
RAID.

Once you have a RAID device, you treat that like a partition on a single
disk--create a filesystem or a LVM physical volume on it. It might be
the case that you can partition a software RAID device, but I haven't
tried that and it doesn't sound right to me. Instead I made a RAID
device for each "partition" that I wanted.


3. Partitions or RAID devices can contain filesystems or LVM
physical volumes.

Yes, which is what I believe I added above.

Right, but I understood your question as whether a RAID device can
contain partitions. That's what I don't know, but I don't think so.


So on a system where there will never be any disks added or partitions
resized, is the extra complexity (abstraction) worthwhile?

It depends on your needs. It's much easier to reallocate space among
filesystems in LVM than it is if each filesystem is on a separate
partition. Do you need that capability? (I have found it handy on
occasion, even for workstations.)


How about recovering from a disk failure? Does this layer above RAID
complicate the process of rebuilding an array?

It doesn't affect the array, because the array is at a lower level.
There can be issues with recovering damaged LVMs because the filesystems
on logical volumes need not be contiguous, but that's independent of
whether they are built on arrays or not.


Thanks,
Alex


--
Matthew Saltzman

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