I have a performance problem about parallel IO on striped logic volume. I build a striped LV on 4 scsi disks. If I do sequential IO on one disk with buffer size 4k, the bandwidth is 9MB/s. Then I do sequential IO on LV with buffer size 16k. Theoretically I can get almost 4*9=36MB/s because LVM stripe 4k IO on every disk but I only get 18MB/s. I don't know where I lost so much performance or it is the overhead of LVM? I do believe LVM do parallel IO because if I increase buffer size to 1024k, I can get 51MB/s which is close to 4*14 MB/s and 14MB/s is the maximum bandwidth of a single disk. My question is why I can't see nearly linear scaling of the bandwidth when the buffer size is small? Does striping LVM do real parallel IO similar to software RAID0? --xiaoxiang
