Low read performance when using /dev/md* devices

[<debian@xxxxxxx>]

Hi,

I got very low read performance when I'm using /dev/md* devices (software
RAID0). The write performance is twice the read performance.

My configuration is two USB 2.0 hard drives on separate USB 2.0 controller
ports.


Case 1:

Using /dev/md* directly on the /dev/sda and /dev/sdb devices gives 20MB/sec
with both read and write operations. However, when using:


Case 2:

# losetup -e aes256 /dev/loop1 /dev/md1
# mount /dev/loop1 /mnt/hd

gives 18 MB/sec performance on write operations, but 10 MB/sec performance
on read operations.


What's wrong?


/Mr. Ericsson


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