[linux-lvm] Re: Software raid on top of lvm logical volume

Michael T. Babcock mike at mikebabcock.ca
Tue Nov 2 15:46:57 UTC 2004

Erik Ohrnberger wrote:

>This solution would seem to be as the holy grail in that it would give you
>the best of all worlds: resizable RAID storage.  Or am I wrong about this

I've been trying to figure out a reason why it wouldn't be doable for a 
few weeks now.

Currently, one can create RAID-0 like performance with LVM2 by 
specifying stripes for one's LVs.  Why not:

lvcreate -L 3GB --raid-level 5 --stripes 3 -n SafeData VG001 /dev/sda 
/dev/sdb /dev/sdc

PV section 1 on sda and sdb are data, section 1 on sdc is XOR data.  PV 
section 2 on sda and sdc are data, and XOR data on section 2 of sdb, and 
so on.

One of the major performance implications would be the larger block 
sizes being dealt with; many people seem to find smaller stripes better 
for performance in RAID-0/5 situations, and by default one would have 
4MB stripes.  With some effort, I'm sure this could be rectified as well.

Thoughts?  Or should I blog about it instead? ;-)

If I didn't have multiple out-of-town server and firewall installations 
this week, I'd code instead :-)
Michael T. Babcock

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