Given that RAID1 writes two copies of the data, my understanding is that reads should be close to twice that of a single disk.
I have tested read performance of different technologies (mdadm, zfs, btrfs) with little success.
From my experience:
- btrfs only used one disk during reads
- zfs/mdadm used both disks however the read speed achieved was that of a single disk
I've verified the results using dd, iotop and iostat.
How can data on both disks be read at the same time in order to achieve twice a single disk's read performance?