LSI Fastpath key, what does it do and how does it do it

[mobilenvidia]

The LSI Fastpath software key is an allusive feature.
It's not mentioned anywhere in any of LSI's utilities, webBIOS or MSM.

It's a very good feature I'm told, but how do we take advantage of it.
I've had a look around and found the MegaRAID® SAS Software User Guide
A behemoth PDF with all sorts of stuff in it.

But to enable Fastpath you basically need to do this:

11.6 Fast Path Advanced Software
MegaRAID Fast Path is a high-performance I/O accelerator for the CacheCade software drive groups connected to a MegaRAID controller card.
The CacheCade software has a read performance advantage over HDDs and uses less power.
This feature dramatically boosts storage subsystem bandwidth and overall transactional application performance when used with a 6Gb/s MegaRAID SATA+SAS controller.
The Fast Path feature supports full optimization of the CacheCade software and hard disk drive (HDD) virtual disk
groups to deliver an improvement in read and write IOPS that is three times greater than MegaRAID controllers not
using Fast Path technology. Also, the Fast Path advanced software is faster and more cost-effective than current
flash-based adapter card solutions.

11.6.1 Setting Fast Path Options
Perform the following steps to use the Fast Path advanced software:
1. Select the Logical tab on the MegaRAID Storage Manager window for the Logical view.
2. Select a virtual drive icon in the left frame.
3. Select Virtual Drive > Set Virtual Drive Properties on the menu bar.
The Set Virtual Drive Properties dialog appears. It shows the default settings for the Fast Path advanced
software:
— Write Policy: Write Thru
— IO Policy: Direct IO
— Read Policy: No Read Ahead
— Disk Cache Policy: Disabled
— Strip Size: 64KB
4. Click OK.
A confirmation dialog displays.
5. Select the Confirm check box, and click Yes to confirm that you want to set the virtual drive properties.

So looking at the above you are basically by passing the cache on the controller.
The software in the Firmware should with the above settings use the Fastpath feature.

I'll attempt to do some tests and see how I get on.

 

[mobilenvidia]

First test:

IBM M1015 in LSI9211 IR mode
4x 2TB Hitachi 7k2000
setup as RAID0
Drive cache = off

Here is default performance as it would be on any non cached controller.

 

[mobilenvidia]

Now the same 4 drives on the LSI9266
No other drives on the 9266, so no chance of Fastpath or Cachecade being enabled.
— Write Policy: Write Thru
— IO Policy: Direct IO
— Read Policy: No Read Ahead
— Disk Cache Policy: Disabled
— Strip Size: 64KB

Similar read performance as the M1015
Write performance a little slower, quite odd, LSI9266 is faster in everyway possible except latency where the M1015 may have a slight edge.

 

[mobilenvidia]

Adding 2x SSD's makes no difference in scores
Making the 2x SSD's a RAID0 array makes no difference in score
Setting 'SSD caching' to on (for Cachecade association) makes no difference to score

Making 2x SSD's RAID0 CacheCade Array
First time run:

2nd time run

Subsequent test yield pretty well the same results.
SSD caching is doing a great job at small files and being able to dish them out quickly from the much faster SSD access times.

But I'm still confused what Fastpath is.
The above was achieved using CacheCade array setup.
Is fastpath just the software part of the cachecade array ?

 

[mobilenvidia]

To dig a little deeper on how this works
I've changed the 4x 2TB RAID0 array to:
— Write Policy: Write Back
— IO Policy: Cached IO
— Read Policy: Always Read Ahead
— Disk Cache Policy: Disabled
— Strip Size: 64KB

No CacheCade (removed the 2x SSD's)

With Cachecade

Cachecade is destroying Sequential reads but, 4k reads/writes are boosted big time
Sequential writes are taking a big hit with Cachecade

 

[mobilenvidia]

Now looking at post 4 scores and comparing with Post 5 scores.

Setting the HDD array to Fastpath specs (disable the spindles to use the cache) reaps very large 4k performance.
Basically the OS is shown the spindle drive but has to go through the Cachecade array (hidden) where Fastpath does its trickery
The small file speed gain is quite exceptional, and ideal for a database server or the likes.

But if you have a server with lots of large reads and writes then a non Fastpath and non Cachecade (ie just a controller with cache) setup is a much better solution.
Cachecade does not favour sequential reads.

Fastpath = brilliant for small files read and written, huge boost.
I would think the faster the SSD the better the results.

I hope this goes to explain what Fastpath is, I've learned a lot from writing it.