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I currently have LVM on software RAID, but I'd like to ask you what you think it is better solution, maybe some pros and cons?

Edit: It is about software raid on lvm or lvm on software raid. I know than hardware raid is better if we are thinking about performance.

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7  
lvm on raid. raid on lvm is the devil's work. -- no reasoning. –  Sirex Dec 31 '10 at 13:12
    
well, hw raid is not necessary better that sw raid. It depends on several factors. If it not a high-end one it is usally worse than linux sw raid (aka mdadm). Regarding management, stability and performance. –  cstamas Feb 24 '11 at 1:34
    
@cstamas: I agree, because cheap ones are usually actually software raids. –  Ency Feb 24 '11 at 6:46

5 Answers 5

up vote 23 down vote accepted

Your current setup is like this:

| / | /var | /usr | /home  |
 --------------------------
|       LVM Volume         |
 --------------------------
|       RAID Volume        |
 --------------------------
| Disk 1 | Disk 2 | Disk 3 | 

It's a much simpler setup with more flexibility. You can use all of the disks in the RAID volume and slice and dice them whatever way you like with LVM. The other way isn't even worth thinking about - it's ridiculously complicated and you lose the benefits of LVM at the filesystem level.

If you tried to RAID LVM volumes, you would be left with a normal device without any of the LVM volume benefits (e.g. growing filesystems etc.)

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Your current setup is fine. This is the recommended way to do it.

Raid deals with keeping the bits secure/redundant/fast/whatever and LVM helps you present them in a esasy to use way.

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have hardware raid and you can have lvm on top - best combination.

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I am assuming you mean Hardware RAID with LVM on Top, vs. LVM and Software RAID on top of LVM. If so, I always advise to opt for hardware based RAID first. Software RAID is just that, while overhead is small, hardware RAID performance will be better 9 out of 10 times. Of course, the methodology will very much depend on your final goal. What are you trying to achieve (performance, protection, etc., etc.)

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"lvm and software raid on top of LVM" -- Now that's an exotic setup ! –  Sirex Dec 31 '10 at 13:50

I think it makes sens to use RAID over LVM if you want to split your disks between a RAID 0 volume and a RAID 1 volume.

With this you can't realocate space between RAID0 and RAID1

| / | /var | /usr | /home  |
 --------------------------
|       LVM Volume 2       |
 --------------------------
|    RAID 0   |   Raid 1   |
 --------------------------
| Disk 1 | Disk 2 | Disk 3 |

With this you can

| / | /var | /usr | /home  |
 --------------------------
|       LVM Volume 2       |
 --------------------------
|    RAID 0   |   Raid 1   |
 --------------------------
|       LVM Volume 1       |
 --------------------------
| Disk 1 | Disk 2 | Disk 3 | 

the good thing is that you can also still move the LVM Volume 2 logical volumes between raid 0 et and raid 1 volume, by using pvmove command

the bad thing is that the setup is complex It would be better if LVM had a better integration of software raid features.

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2  
I don't know enough storage goodies to say why this is a bad idea, but it leaves me quite unsettled and a distinct feeling of dread. –  Scott Pack Nov 7 '12 at 16:15

protected by Chris S Apr 29 '12 at 22:07

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