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From: Arno on 6 Apr 2010 16:53
Bob Willard <BobwBSGS(a)trashthis.comcast.net> wrote:
> Arno wrote:
[...]
>> RAID5/6 is more I/O intensive. CPU load does not matter even
>> there, unless your CPU is really, really slow or you have
>> a RAID6 with 2 drives missing. Just to give you a number,
>> my old AMD Athlon64 X2 5600+ does 5.2GB/s for an undegraded,
>> Linux software RAID6. So you need something like 20 current
>> SSDs in one RAID6 array to saturate one core.
>>
>> What does matter is that you have a fast datapath to the
>> controller. PCI-E attached SATA controllers are typically
>> fine.
>>
>> Arno

> Interesting. Have you measured the CPU overhead caused by
> continuous writes to a software-based RAID5/6 RAIDset on
> relatively current CPUs? I ask, because I have not had the
> opportunity to do so for a few years.

Sorry, this is just the boot-time benchmark that Linux does.
I do not have a RAID5/6 running at the moment, just RAID1
(one of them 3-way) arrays. But I supect these numbers are
accurate and will give you something like <10% CPU for
continuous writes on a 4 disk RAID6 and maybe around 20%
on a 8 disk one. I may have a chance to run benckarks on
a 8 disk Software RAID6 in the next few days though. Will
post in that case.

Arno
--
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno(a)wagner.name
GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F
----
Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans
From: Rod Speed on 6 Apr 2010 18:05
William R. Walsh wrote

>> What types of drives can be used in AHCI mode?

> Any serial ATA drive can be used with a host controller operating in AHCI mode.

> The difference is mainly for the software that works with the drive.
> An operating system will likely need a driver to recognize the serial
> ATA controller when it's running in AHCI or RAID mode.

>> What types of drives can NOT be used in AHCI mode?
>> Are there any Windows XP AHCI drivers?

> You get the drivers from your hardware, chipset or
> motherboard manufacturer. For Windows XP and earlier,
> you will need to slipstream them (difficult from what I hear

Nope, very easy.

> -- never tried it) or have a 3.5" floppy diskette with the drivers available at setup time.

>> Does this mean that if you have two drives in a mirrored RAID,
>> you cannot use any optical drive or any single hard drives on
>> the motherboard ports? Thank you in advance for all replies.

> See your chipset or motherboard maker's documentation for the
> absolutely correct (well, hopefully) answer. My experience with real
> hardware RAID controllers has shown that you can have optical (and
> other) drives attached. However, the "RAID" built into a chipset is
> not "real" hardware RAID. Still, CD-ROMs and most other serial
> ATA drives are probably supported. It's easy to find out if you have
> the hardware there, and no harm will come from your trying it.

> The RAID utilities you will have access to should not have a problem
> configuring a "container" that has only a single drive in it.
> However, you should not be fooled into thinking that this drive will
> have a standard format readable from any other serial ATA controller.
> It probably won't.


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