LVM Mirroring failure notification

Mike Lovell mike at dev-zero.net
Tue May 12 11:18:04 MDT 2009


Aaron Toponce wrote:
> On Tue, May 12, 2009 at 02:46:23AM -0600, Mike Lovell wrote:
>   
>> So I have a box that I want to use 6 drives with lvm on for xen virtual  
>> machines with. While experimenting with things, I found that I can just  
>> do a pv for each disk and then add -m1 to lvcreate to do a mirror. The  
>> question I have is how can I make things automatically notify me by  
>> email if one of the drives, that has parts of a mirror, fails? I am  
>> liking using LVM mirroring in this situation but I it doesn't help me a  
>> lot if I don't know when a drive fails. Thanks for any help.
>>     
>
> Wait, let me get this straight- you have 6 drives, and you're using RAID
> level 1 through LVM? You know what that means, right? You've just lost 5
> disks worth of space. Why not just give the 5 disks to me? I could put
> them to good use. :)
>
> Unless you need that extreme redundancy, I would suggest starting over
> using Linux software RAID beneath LVM. With 6 drives, I would do RAID
> level 6 with all active in the array. Then, you're utilizing a decent
> amount of disk space for your 6 drives, and should a drive fail, you'll
> deprecate to RAID 5, which works well.
>
> Just a thought.
>   
I'm not trying to do a 6 drive raid 5. Doing a -m1 creates one copy of 
the new LV. So in this case, I would lose the equivalent of half of the 
storage space which would be the same as doing a RAID10.

The particular case I am looking at this for is for a VG for many Xen 
virtual machines with each virtual machine having an LV. If I were to do 
a RAID10 underneath LVM, IO access for a single virtual machine would 
touch all 6 disks in the array. But if I just use LVM to also create a 
single mirror, IO access for a virtual machine would only touch 2 of the 
disks (technically 3 if you include the mirror_log). I don't need the 
performance gains that doing the RAID0 part would give me and so I am 
hoping to remove one layer. But I need to receive a notification when a 
disk dies. I have used a RAID10 on a similar box and it worked okay but 
an experimenting with something else. So does anyone know of a way to do 
notifications if a PV in LVM dies?

mike



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