Re: [gentoo-server] RAID

[Josh Wyatt]

Jesse, Rich wrote:
> It depends.  I'd like to see SW RAID keep up with dual 2GB fibre
> attached to an IBM FAStT600.  Then again, I haven't been given a budget
> to test this with a Linux server.  :)

I have seen four FAStT600's spread across 20 x445s doing software RAID, and it is substantially faster than hardware RAID.
Thanks,
josh


>
> Also remember which RAID you're talking about.  If you need parity, see
> my previous post about BAARF.
>
> Finally, saying the CPU is not usually the bottleneck in a database
> server is misleading at best.  Being mainly an Oracle DBA these days,
> faster CPUs can *cause* CPU contention.  Like I said before, "it
> depends".  And like everything else, YMMV.
>
> Rich
>
> -----Original Message-----
> From: Sean Cook [mailto:scook@×××××.net]
> Sent: Wednesday, February 01, 2006 3:39 PM
> To: gentoo-server@l.g.o
> Subject: Re: [gentoo-server] RAID
>
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> kashani wrote:
>
>>Sean Cook wrote:
>> > Redhat In their manual:
>>
>>
>>>"With today's fast CPUs, Software RAID performance can excel against
>>>Hardware RAID."
>>>
>>>As I stated before, it depends on where your bottleneck is... if you
>>>are not cpu bound, software raid is great! and will boost IO through
>>>put on comparable hardware.  If you are already CPU bound, forget
>>>software raid, it will degrade your system to a crawl...
>>
>>
>>Badly done tests circa 1998 without any sort of methodology, mention
>
> of
>
>>cluster sizes, etc is proof than any idiot can make a computer slower.
>>
>>    I'll argue that a fully supported hard raid card is always
>
> superior
>
>>to a software raid by it's very nature, having local I/O cache and a
>>dedicated chip. However there are definitely workloads where a
>
> software
>
>>raid is good enough that spending money on a hardware raid card is
>>pointless. I can not imagine a case where all things being equal that
>>software raid would be measurably faster.
>>
>>    In the event that removing your RAID card makes your disk 5x
>
> faster
>
>>I'd also recommend removing the admin who setup the original system as
>>well. :-)
>>
>>kashani
>
>
> My post did say "Back in the Day" and it was around 1999 that we did
> this however, then I was running unstable raid tools and they have come
> a long way, and I was running 2.2 kernel.
>
> However, the only people I am aware of that say the performance is
> better on hardware raid are hardware raid manufacturers and you... You
> don't work for LSI do you?  Most of the linux software folks agree with
> me or take a mildly more conservative tone.
>
> eg:
>
> Redhat Enterprise Linux (circa 2005-2006)
> http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/pdf/rhel-isa
> -en.pdf
>
> Often the excess CPU power available for software RAID parity
> calculations greatly exceeds the processing power present on a RAID
> controller card. Therefore, some software RAID implementations
> actually have the capability for higher performance than hardware RAID
> implementations.
>
>
>
> Mysql:
>
> Hardware Versus Software
>
> Some operating systems can perform software RAID. Rather than buying a
> dedicated RAID controller, the operating system's kernel splits the I/O
> among multiple disks. Many users shy away from using these features
> because they've long been considered slow or buggy.
>
> In reality, software RAID is quite stable and performs rather well. The
> performance differences between hardware and software RAID tend not to
> be significant until they're under quite a bit of load. For smaller and
> medium-sized workloads, there's little discernible difference between
> them. Yes, the server's CPU must do a bit more work when using software
> RAID, but modern CPUs are so fast that the RAID operations consume a
> small fraction of the available CPU time. And, as we stressed earlier,
> the CPU is usually not the bottleneck in a database server anyway.
>


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