hpacucli gives 'Max array count reach' with HP Smart Array P420i raid controller on DL360p Gen8

[Decstasy]

Hello Asif,

>>> You could keep the md raid but you will have more perfamnce
>>> withoud the md raid.
>> 
>> Can you please explain why hardware raid controller will give higher
>> performance?

There are several circumstances why it is faster and better to use the 
raid 10 functionality via the controller... I will just mention the two 
most important facts:
1. The controller itself has a little CPU which is especially designed 
to provide raids (a asic chip [Application-specific integrated 
circuit]). It can handle everything better and more efficient than your 
cpu.
2. Your software Raid 1: When you write something to your md raid, your 
Linux is going to mirror it to two devices which are on the same 
controller BUT different logical drives on your controller and this are 
different scsi bus addresses.
So your controller which could do all the work gets doubled data via the 
bus to write it on two devices. Writing a 5GB file would mean 10GB of 
data via the bus to your controller and your controller treats every 
logical drive independent, so your raid controller has to calculate and 
write the stripe also twice. The redundancy should be generated by the 
raid controller and not from the system - you're wasting your resources 
and you're load gets higher while just writing something to your disk...

To understand this in detail you should read something about how linux 
treats devices and how the hardware "units" communicate to fulfil the 
command to write something on your disk.
You can read here a little bit more about it: 
https://www.adaptec.com/nr/rdonlyres/14b2fd84-f7a0-4ac5-a07a-214123ea3dd6/0/4423_sw_hwraid_10.pdf

I know that this is just "basic stuff" but I hope I helped you :)


Best Regards,
Dennis