mdadm mirrored RAID1 performance using RAID10 -f2 (Far Layout) is the solution
The only way I've found in mdadm to make 2 drives perform like a proper RAID 1 (eg. the read speed should be 2x that of a single drive) is to use the --layout=f2 (far 2).
mdadm raid10 performance issues.
Be very aware that mdadm seems to default to layout=n2 (which means near). In this scenario it means it is like mdadm RAID 1 performance (you get maximum read speeds of a single drive).
dd if=/dev/md126 of=/dev/null bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes (2.1 GB) copied, 6.46397 s, 180 MB/s
Now look at the difference in the same drives in layout=f2 (which means far).
dd if=/dev/md126 of=/dev/null bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes (2.1 GB) copied, 6.46397 s, 324 MB/s
As we can see the speed is nearly double (a small amount of bandwidth appears to be lost as overhead due to mdadm)
Tags:
mdadm, mirrored, raid, layout, solutionthe, ve, eg, default, maximum, speeds, dd, dev, md, null, bs, bytes, gb, copied, mb, bandwidth, overhead,