I recently added a new hard drive to my desktop and reorganized the partition structure. In doing so I wanted my /home partition to be mirrored for safety, but I also wanted to use lvm to make managing my multiple partitions less painful. In my research, I found there are basically two ways to do this. One is to create a linux RAID1 device from the two drives and then use that device as a physical extent in a lvm volume group (here is a basic tutorial). The other method is to us LVM2′s mirroring capabilities. I personally would rather use the latter solution if there is no performance impact since moving the partitions around later would be much easier, however what I read gave the impression that LVM2 mirroring would be slower.
To test this, I setup a quick informal benchmark. I created 2 partitions on each of two drives and set one up as plain raid1 (no lvm) and the other as lvm with a mirror. I then ran bonnie++ on each of the partitions. The results were surprising. MD RAID1 gave about 25MB/sec write and 50MB/sec read. However LVM2 mirrored gave about 50MB/sec write and 55MB/sec read. Since the test was not perfectly sterile (there were other processes running at the same time) I would be willing to give these number +/- 10MB/sec. However still, LVM write was considerably faster than MD RAID1. I so far have no explanation for this, but will test further. If anyone has an explanation, I’d be happy to hear.