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whukes

Member

Registered: 2008-07-18

Posts: 34

LVM vs. RAID

Hello all.  I have plans to build a large file server for some media content.  I had a few questions about LVM and RAID. 

I would like to have at least 8 1TB hard drives in the server. I started researching about RAID5 and RAID6 to accomplish my goal of one large volume.  I was wondering in my situation if it wouldn't be easier to just use LVM instead.  I like the idea of using LVM because I won't loose any space because of redundancy.  What I am unclear about though is if a drive in the VG fails, do I loose all my data or just the data on that one drive?

Is there any real benefit to using raid over lvm in my situation?  Loosing 1TB due to drive failure would not really bother me too much because the data isn't all that critical and could be easily replaced.

Thanks for your thoughts.

rine

Member

From: Germany

Registered: 2008-03-04

Posts: 217

Re: LVM vs. RAID

LVM and Raid aren't mutually exclusive. You can use both at the same time, LVM for flexibility and Raid for redundancy/speed.

iBertus

Member

From: Greenville, NC

Registered: 2004-11-04

Posts: 2,228

Re: LVM vs. RAID

Bottom line, if you are planning on having 8 drives, use RAID. If one drive fails in a JBOD setup you will loose the entire filesystem. Your odds of suffering a drive failure goes up with an increasing number of drives. Also, do some research on the RAID5 non-recoverable read error problem that is popping up now with consumer grade discs of that size. Consider RAID10 (the linux MD implementation is very good) or RAID6.

whukes

Member

Registered: 2008-07-18

Posts: 34

Re: LVM vs. RAID

So it would be possible to build a raid5 or 6 array and then add say 4 more TB to it using LVM?  If one of the added drives fails, does that hurt the raid array?

Last edited by whukes (2009-03-21 01:38:13)

rine

Member

From: Germany

Registered: 2008-03-04

Posts: 217

Re: LVM vs. RAID

Adding to the volume group should work without problems, as easy as "lvextend <vg> /dev/sdx" or something.
If one (two with raid6) drive fails, your system will still work. It's vulnerable then, because the next drive failure will kill everything, so you should have a spare hard drive lying around for replacement. The raid (the parity stuff) then gets rebuild automatically. (that will take some hours).