Re: Hardware vs. Software Raid Speed

[Joel Jaeggli <joelja@uoregon.edu>]

Marc Perkel wrote:
> 
> 
> Tejun Heo wrote:
>> Andre Tomt wrote:
>>> Marc Perkel wrote:
>>>> Running Linux on an AMD AM2 nVidia chip ser that supports Raid 0
>>>> striping on the motherboard. Just wondering if hardware raid (SATA2) 
>>
>> SATA2 has nothing to do with hardware RAID.
>>
>>>> is going to be faster that software raid and why?
>>>
>>> Beeing a consumer type board (AM2), the "raid on the motherboard" is
>>> in 99.999% of the cases just software raid implemented in their
>>> Windows drivers, a bootup setup screen plus some BIOS magic to get
>>> the OS booting.
>>
>> And, yeah, they're all software RAID.  Also, there isn't much to be
>> gained from making RAID0/1 hardware.  The software overhead isn't that
>> big.  For RAID5, having XOR done in hardware helps.
>>
> 
> Thanks - I suspected that Raid 0 didn't gain anything in hardware unless
> they provided additional buffering or something but I just thought I'd
> ask in case there was something I was overlooking.

A hardware raid controller can buy you a battery backed write cache, so
there are potentially some performance/safety benefits potentially.

We have a mix of software raid and 3ware based hardware raid subsystems.
For the applications we support, in general I can say that performance
was not the discriminating reason to choose one over the other.

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Joel Jaeggli             Unix Consulting              joelja@uoregon.edu
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