[olug] To RAID or not to RAID

[Obi-Wan]

On 09/22/2014 09:31 AM, Christopher R. White wrote:
> I am in the process of building a new home server.  I've finished
> collecting all the parts and am at the put it all together stage.  This
> will be an all-in-one home server to hold my media, photos, PC backups,
> etc.  i want to make sure I have data redundancy factored in before I move
> ahead.  In the past, I've always used software RAID but I'm looking at LVM
> as an alternative.  I currently have 2 drives but the thought of adding
> more is always in the back of my mind (hence the idea for LVM).  What is
> your experience with LVM?  Pros, Cons, something I'm not considering?!

I've got somewhere north of 10TB in my desktop machine, spread across 
six drives.  One's the boot/OS disk, but the other five are a 
mis-matched hodge podge of drives that were each top of the line when I 
bough them over the past several years.

Those five "data" drives hold all of the non-OS data on my system. 
They're seen by the OS as three filesystems, configured as follows:

* A 1.5TB partition on each drive gets combined to create my "photo" 
filesystem.  The smallest drive is only 1.5TB, hence the choice of 
partition size.

* The three larger drives each also have a 500GB partition that gets 
combined into my "home" filesystem, which contains all my personal stuff 
other than digital photos.  The next-smallest drive is 2TB, and had only 
500GB left after the initial 1.5TB partition was carved out.

* One remaining drive still had another 1TB left, which gets used by 
itself to store my DVD rips that are easily recreated if I lose that disk.

For years, the two multi-disc filesystems were just concatenated 
together using LVM so that I could extend them by adding another drive 
to the system.  That worked well enough, but every time I lost a drive, 
I had to extract everything off backup, which takes a very long time for 
that much data.  When I finally filled all the drive bays in my chassis, 
I decided to give up my ability for dynamic expansion and instead use 
mdadm to implement RAID5 on the two important filesystems.  I haven't 
lost a drive yet under that setup, so I can't say how well it works, but 
I definitely prefer the thought of not having my machine go down for a 
couple days when a drive does fail.

So I guess my advice to you depends on your uptime requirements and your 
backup capacity.  If you don't have very much data and you can tolerate 
being down for a while until you replace a failed drive, then just use 
LVM.  It's a lot easier to work with than mdadm, IMHO.  If you can't 
afford to be down very long and/or you have tons of data to restore, 
then use mdadm RAID on your drives.

-- 
*Ben "Obi-Wan" Hollingsworth* obiwan at jedi.com <mailto:obiwan at jedi.com> 
www.Jedi.com <http://www.jedi.com>
The stuff of earth competes for the allegiance I owe only to the
Giver of all good things, so if I stand, let me stand on the
promise that You will pull me through. /-- Rich Mullins/