RAID1 performance with madam

Single-threaded application performance on mdadm RAID1 is indeed no better than using a single disk. That's because mdadm chooses one of the disks in the array to satisfy a given read request. So if your workload consists of a single process reading sequentially from a single file, then mdadm RAID1 will not outperform a single disk.

However, if your workload instead consists of many parallel file accesses---such as would occur in a file server being hit by multiple users at once---then RAID1 will be faster than a single disk because the concurrent read requests are allocated across multiple disk spindles.

In summary, whether or not mdadm RAID1 will be faster than a single disk depends a lot on your particular mix of workloads.

The "far" layout may give you better read performance (see http://neil.brown.name/blog/20040827225440). Apart of that RAID1 with md gives redundancy, but no speed boost.

Edit: For read performance play with readahead (i.e. increase it. A lot.) . It can work wonders.