[BozemanLUG] Questions on RAID & LVM

[Brian Vincent]

LVM sits on top of the metal.  Someone else will answer in more detail to your specific questions, but I'll throw out some generalizations.

LVM is nice because down the road you can easily chance the size of how the OS sees the size of the partitions.  Later if you wanna throw more disks in the mix, you can just allocate the physical disks as you need.  If you have hardware RAID, you might have some mirrored drives that the OS is just seeing as a single disk.  Figure out your RAID as a first step, then layer LVM on top.  You mentioned you didn't want to rehash the hardware/software RAID thing, but I'll recommend using hardware RAID.

I really like the idea of virtualizing everything.  Throw VMWare's ESXi server on there first, then build everything on top; it makes migration later a snap.  We're having a lot of success in that, though you'll probably need to buy some vSphere licenses to manage it.  It adds another layer of complexity at negligible performance impacts (at least for file serving) and it lets you pull out the rug from underneath the OS later. 

Whatever you do, if you get into setting up even a few partitions with LVM, leave some of your physical disk unallocated so you can grow a volume later.

-------------

Brian Vincent
Moonlight Basin Technology
bvincent at moonlightbasin.com
406-539-0569

________________________________________
From: discuss-bounces at bozemanlug.org [discuss-bounces at bozemanlug.org] on behalf of R. Potter [rpotter at zoncko.com]
Sent: Sunday, September 12, 2010 11:17 PM
To: Bozeman Linux Users Group
Subject: [BozemanLUG] Questions on RAID & LVM

I really don't have much experience with RAID and LVM and I am faced
with playing with both technologies.

I am setting out to build a total of 3 servers.  These servers will be
built using Ubuntu and software RAID.  I am not looking to have the
hardware/software debate, but I am looking for some guidance and
insight.  I am  hoping some of you can offer that.

Server one: built using HP ProLiant with QuadCore Xeon, 4 GIG's of RAM
and two 1 TB Hard drives.  Server can take four 1TB HD's but nothing
over 1TB per drive.  Corporate suggested I build this using an LVM so
that if need be I can expand the capabilities.  However, I am only
planning on running RAID 1 with this system.  This storage server will
hold data for two departments who currently are storing just shy of 100
GIG's.

Server two & three: Both of these remaining two servers will be
dedicated to one department each and both departments are currently
storing slightly more than 500 GIG's.  That means I need to either find
servers that have no 1TB per drive limit, or I need to purchase four 1
TB HD's and plan to run RAID 1+0.

Question 1: If the first server is only storying 100 Gig's after roughly
2 or 2 1/2 years and current configuration without LVM would be a 1 TB
RAID 1 system, Is there any benefit to setting up an LVM?

Question 2: Like question one, is there any good reason to setup an LVM
on the other two servers if server is maxed out on qty of HD's and total
HD capacity (4 x 1TB)?

Question 3: I have been reading the Ubuntu instructions for setting up
the software RAID and the instructions pretty much walk you through the
process.  But then after the RAID instructions are complete they offer
the LVM instructions but the LVM instructions make it sound like you
don't setup RAID first.  Is that a correct understanding, that LVM come
before RAID?

Question 4: Based on question 3, if I am understanding the LVM
instructions, I would setup the two or four HD's as individual drives,
then setup LVM followed by RAID on top of the LVM - or RIAD'ing the
LVM.  Would that be correct?

Question 5: The instructions from Ubuntu indicated that there were three
types of LVM, Volume Group, Logical Volume, and Physical Volume.  If I
should setup an LVM based system, which of the three types of LVM would
you all recommend?

I know there are several questions and most of them probably will
require more than one word answers, but if any of you have the time to
share your experience/view points I would appreciate it.

Thank you,

Rob Potter
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