[DRBD-user] DRBD 0.7.23 over MD raid performance

[Laurent CARON]

Hi,

I did set up two machines with drbd, heartbeat, raid ... and i'm still
wondering why the read throughput using drbd is as much as 4 times less
than using md.

hdparm -tT /dev/md2

/dev/md2:
 Timing cached reads:   6496 MB in  2.00 seconds = 3251.89 MB/sec
 Timing buffered disk reads:  1114 MB in  3.01 seconds = 370.59 MB/sec

hdparm -tT /dev/drbd0

/dev/drbd0:
 Timing cached reads:   6532 MB in  2.00 seconds = 3270.07 MB/sec
 Timing buffered disk reads:  322 MB in  3.01 seconds = 106.88 MB/sec

Please note that md2 is the underlying device that holds drbd0

Thanks

Laurent