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Old 08-29-2009, 04:47 AM   #1
geek.ksa
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RAID over LVM


hi,
is it possible to implement RAID over LVM LVs? say I have two logical volumes, can I create a RAID device over them?

Thanks
 
Old 08-29-2009, 05:13 AM   #2
kdelover
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I think its best to create raid first then do lvm over it .
 
Old 08-29-2009, 05:38 AM   #3
EricTRA
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Hello,

You cannot implement RAID (Redundand Array of Inexpensive Disks) over LVM (Logical Volume Manager.

RAID is an array build on several (at least two) physical disks.
LVM lets you create groups of those disks, logical volumes on the physical volumes, etc...

So if you want redundancy on disk level, implement RAID, install your linux with LVM support and voila, up and running.

Kind regards,

Eric
 
Old 08-29-2009, 05:51 AM   #4
kdelover
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i'll just post my query here,since it deals with lvm and raid.I was planning to do the same thing for one of my linux media servers and do a raid then do lvm,the issue is i have 4 HDDS one is 20 GB(IDE) ( almost 8 yrs old ) and an 80 GB(IDE) + 2x1 TB SATA drives,will there be any performance issues here since the 20 GB one is 5200 RPM and rest are 7200 RPMS?
 
Old 08-29-2009, 08:58 PM   #5
r3sistance
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Hi kdelover, you should really have raised a seperate thread for a different query. But to answer your question, yes this is likely to cause issues since the drives in the raid won't be fully syncroised due to the different speeds of the disks. Else wise the disks will all have to drop to fastest speed of the lowest disk (5200 RPM) what would be overall the faster disks would lose performance. I'd advise generally building raids with same speed, same size disks if possible, speed is more important then size tho.
 
Old 08-29-2009, 10:55 PM   #6
ongte
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Running Linux software raid over LVM volumes is actually entirely possible, but makes no sense, since it offers no redundancy.

LVM2 actually has some built-in RAID capabilities like stripping. It might be worth exploring if you are looking to increase performance.
 
Old 08-30-2009, 05:05 PM   #7
geek.ksa
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Quote:
Originally Posted by ongte View Post
Running Linux software raid over LVM volumes is actually entirely possible, but makes no sense, since it offers no redundancy.
how could it offer no redundancy when you have two logical volumes always synchronized?. My problem is that i have one HDD on my machine and LINUX RHEL 5 designates it entirely as a VG (volume group), I honestly didn't know how shrink the VG and free some space so that I can create some other non-lvm partitions. So i am left with the option of creating logical volumes within the VG which I was wondering if I can implement RAID over them.

But yeah I'll research more on LVM raid capabilities.

Thanks all
 
Old 08-30-2009, 06:11 PM   #8
r3sistance
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A single disk raid is almost entirely pointless if that is what you are trying to achieve, you still have a single point of failure and you gain none of the performance increases that can come from using raid, about the only case this would help with is if a LVM corrupts but the most likely way a LVM would corrupt from is resizing and that's an action what is mirrored so... if this isn't what you are talking about then perhaps you would like to expand?
 
Old 08-30-2009, 07:58 PM   #9
chrism01
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@geek.ksa: http://tldp.org/HOWTO/LVM-HOWTO/

As a general comment, raid the physical disk, then treat each raid (eg md0) as a PV to add to a VG etc.
 
  


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