hpacucli gives 'Max array count reach' with HP Smart Array P420i raid controller on DL360p Gen8
dj at decstasy.de
Sun May 8 15:56:25 UTC 2016
>>> 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
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
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:
I know that this is just "basic stuff" but I hope I helped you :)
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