You can either use lvm to stripe or more manually, extent based striping.
lvm will stripe across disks using to methods ...
-i (lvm storts out the stripes)
-D (distributed extent based striping using physical volume groups)
Persoanlly, if possible, I'd blow away the data and then recreate using extent based striping, if you have alternative paths to each physical disk ...
eg. We use mainly XP array or EMC, everything is dual pathed, so for each device, we have an alternate path for resiliance, meaning two HBAs in each server, so if performance is an issue, we can use extent based striping, and by controlling which devices we alternate round, one extent goes thru. one HBA, the next extent thru. the other HBA, so distribute the load across two HBAs. I've seen some amazing performance gains using this (knocked down from 100% to 50%ish).
Martin
Martin