[BozemanLUG] Questions on RAID & LVM

Mon Sep 13 13:00:58 MDT 2010

I concur with the opinion LVM isn't worth the effort, besides, I don't know of a simpler way repartition after a failed drive then: "sfdisk -d /dev/sdb | sfdisk /dev/sda"

I'm of the opinion software raid is always better then hardware raid when you have a non-homogenous hardware environment.  If you go with software you can put a raid set in any device and you're going to be able to make it work, not so if you don't have the same hardware raid controller say Adaptec versus 3ware.  In the times of crisis, I prefer to be able to access my data from anywhere on any hardware.

Rusty

On Sep 13, 2010, at 2:18 PM, Sheldon Ross wrote:

> I'm gonna play a little devil's advocate here, and ask what exactly you are trying to gain by using LVM. [opinion] In my experience, its almost more pain than its worth. [/opinion]  
> If your just looking to span multiple drives with a partition, I'd use RAID 0. If you are using more than 2 drives and want redundancy 1+0.  Of course, that's using hardware RAID which will present the OS with just one visible drive.  Maybe software RAID causes the concern.
> 
> +1 to the Hardware RAID even though you don't want to hear it :)
> 
> Ross
> 
> > From: llc_lug at lcaudell.com
> > Date: Mon, 13 Sep 2010 12:53:08 -0400
> > To: discuss at bozemanlug.org
> > Subject: Re: [BozemanLUG] Questions on RAID & LVM
> > 
> > Though, I'm not in Bozeman anymore, I would agree with Scotts points on LVM, and also suggest you consider the opposite of expanding your drives. What if you were asked to install an enterprise grade DB on smaller partitions. A real pro would want the DB engine on a separate partition from the OS, and another for the data set. 
> > 
> > - Lou Caudell
> > 
> > On Sep 13, 2010, at 11:36 AM, Scott Dowdle wrote:
> > 
> > > Rob,
> > > 
> > > ----- Original Message -----
> > >> 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.
> > > 
> > > Not debating... just sharing info. HP offers some good hardware RAID options in their Proliant line. I have 6 Proliant Dl380 G5 models here at work... and have retired a number of G4, G3, and G2 (G means generation) units. The only ones I had without hardware RAID were the G2 units... but if you already have the hardware and it does not include a Linux compatible hardware RAID card, I guess that really isn't an option for you.
> > > 
> > > The main difference of course is that all of the hardware RAID units make the individual drives transparent to the OS and as a result they are hot swappable... and generally have good idiot lights so you can see if something is wrong... again, without having to have special software installed.
> > > 
> > > Software RAID won't let you do hot swap and doesn't have any idiot lights.
> > > 
> > > Both hardware and software RAID perform well so that really isn't an issue.
> > > 
> > >> Server one: built using HP ProLiant with QuadCore Xeon, 4 GIG's of RAM
> > >> and two 1 TB Hard drives.
> > > 
> > > Those drives are actually quite large for servers. The largest drives I have in an HP at the moment is 146GB and the largest in a Dell is 500GB. Of course they have larger drives now and it has been a couple of years since I've bought anything new. I'm due new hardware next summer.
> > > 
> > >> 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.
> > > 
> > > If you do RAID 1 you'll probably want an extra drive as a hot spare. If you go to four drives you'll probably want to a three drive RAID 5 with a hot spare.
> > > 
> > >> Question 1: If the first server is only storing 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?
> > > 
> > > LVM lets you dynamically resize partitions and add / remove drives / partitions on the fly if the need ever arises. If the need never arises, you really haven't lost anything.
> > > 
> > >> 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)?
> > > 
> > > You could live without it but you gain more flexibility with it.
> > > 
> > >> 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?
> > > 
> > > Man, I haven't done a fresh install of a physical machine in a while... and for servers I use either RHEL or CentOS... and their installers basically let you do everything from the installer and so the order is handled for you. I don't recall much specifics but you might check out their docs just as a point of reference. Sorry I couldn't be more help there.
> > > 
> > > Perhaps you can do so trial installs in a VM until you feel more comfortable with the process. ALthough it doesn't make any sense to make a RAID setup with a single drive, it can be done for learning purposes with multiple partitions on a virtual disk.
> > > 
> > >> 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?
> > > 
> > > Those are really pieces of the same thing... just like a logical partitions are contained inside of an extended partition. I believe a Volume Group is made up of one or more Physical Volumes and that from those you can make Logical Volumes that you basically use as partitions. Again, I a bit rusty because I haven't done it in a while.
> > > 
> > > One really handy GUI tool, and I hope they have it or something like it on Ubuntu, is system-config-lvm. It is what I use post install to see what's there and to resize things. I have dynamically resized partitions a number of times and I've always used system-config-lvm. Of course it can be done from the commandline too.
> > > 
> > >> 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.
> > > 
> > > I didn't really do a good job of answering your questions but hopefully some additional responses will give you some additional information. As with so many things, reading about it can only help so much... and playing with it will really help it all sink in.
> > > 
> > > If you ever want to pay me a visit at work, I can show you how my stuff is setup.
> > > 
> > > TYL,
> > > -- 
> > > Scott Dowdle
> > > 704 Church Street
> > > Belgrade, MT 59714
> > > (406)388-0827 [home]
> > > (406)994-3931 [work]
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Rusty Conover
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