Speed of software RAID 0 with 4 SSD drives is strange

Question

Situation:

I have a server working on Ubuntu Server 16.04. I created software RAID 0 array that contains 4 SSD disks.

When I checked the speed of the RAID array on my server I was confused. I was supposed to see that read speed is about 1200 MB/s (300 MB/s * 4) and write speed is about 1100 MB/s (300 MB/s * 4 - %). But, instead I saw only 860 MB/s for read speed and 80 MB/s for write speed.

I decided to check if this issue is connected to hardware. So, I created RAID 0 that contains 4 SSD disks, but now on my desktop. Every single hardware component is different there + it's Ubuntu Desktop 16.04 (AMD-64).

When I checked the speed of the RAID array on my desktop I saw only 696 MB/s for read speed and 178 MB/s for write speed. So, now I'm sure that it's Ubuntu 16.04 problem or SSD disk problem.

What are the causes of this issue and how to solve it?

Thanks for help

RAID configuration:

1. sudo mdadm --create --verbose /dev/md0 --level=0 --raid-devices=4 /dev/sdc /dev/sdd /dev/sde /dev/sdf

2. sudo mkfs.ntfs -F /dev/md0

3. sudo mkdir -p /mnt/md0

4. sudo mount /dev/md0 /mnt/md0

5. sudo mdadm --detail --scan | sudo tee -a /etc/mdadm/mdadm.conf

Specifications:

Server:

Operating system: Ubuntu Server 16.04 (AMD-64)
SATA Interface: II

Disks:

Type: SSD
Interface: SATA III + SATA II
Capacity: 480 GB
Controller: Phison S11
Read Speed: 560 MB/s
Write Speed: 540 MB/s

• Full specifications you can get there (tab specifications)

RAID:

Level: 0
Devices: 4
File System: NTFS
Read Speed: 860 MB/s (not buffered)
Write Speed: 80 MB/s

Answer 1

I know this is old, but it remains unanswered and probably the best kind of answer we're going to get is as follows:

There are many factors that can impact the performance you get from disks and without further information we're unlikely to know. However given the information provided we could make some guesses.

These days most motherboards support full speed on each SATA controller, so I don't necessarily agree with comments above, but perhaps it was true for your controller.

Not least of which is manufacturers boasting about speeds which are either not correct, or not correct in a sustained way. Even comparing something like a recent Seagate FireCuda with an equivalent Intel or even older - the Intel manages a better more consistent performance and the FireCuda takes almost twice as long for the same task.

I also did come across this thread on Reddit, Buyer Beware: SATA SSD's with Phison S11 controllers, which suggests your SSD's controller specifically as having issues with I/O, however further down it does refer to a different model. I suspect in this case you might have come across this - keeping firmware of the SSD up to date and the motherboard is one of the best ways to remove these kinds of barriers.

To a large extent the file system does not make a lot of difference, but it can if it's not set up well, but again I agree it's not likely this issue.

With SSD's trim can also be an issue that can slow things down. Hopefully you've sorted it by now, but maybe these ideas help someone else coming along this path.