SATA ports on the ASUS M4N78 PRO motherboard?

[Daniel Prince]

I am thinking of buying an ASUS M4N78 PRO motherboard. It has six
SATA ports. The manual says that ports five and six must be used in
RAID or AHCI mode. What types of drives can be used in AHCI mode?
What types of drives can NOT be used in AHCI mode? Are there any
Windows XP AHCI drivers?

The manual also says, "Due to chipset limitations, when you set any
of the SATA ports to RAID mode, all SATA ports run at RAID mode
simultaneously."

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.

 

[Arno]

I am thinking of buying an ASUS M4N78 PRO motherboard. It has six
SATA ports. The manual says that ports five and six must be used in
RAID or AHCI mode. What types of drives can be used in AHCI mode?
What types of drives can NOT be used in AHCI mode? Are there any
Windows XP AHCI drivers?

You have it backwards, the drices do not care, i.e. all work.
The problem here is that (at least on my mainboard), you may
have to use all ports in AHCI if you want ro use the last two.

Win XP AHCI drivers exist, but (it being a stupid MS product)
are not quite easy to install. You see, without AHCI you
cannot install the drivers as XP thinks it does not need them.
With AHCI, XP cannot access the drives, and if your board
is like mine, that means any drive. Pretty braindead.

The manual also says, "Due to chipset limitations, when you set any
of the SATA ports to RAID mode, all SATA ports run at RAID mode
simultaneously."

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.

Possibly. But you should not use mainboard RAID anyways. Better
use software RAID or get a separate RAID controller. You also
should have a spare RAID controller (not needed with software
RAID obviously), if you still want to be able to access you data
in case the RAID controller dies. This does happen in practice.

Arno

 

[Daniel Prince]

Win XP AHCI drivers exist, but (it being a stupid MS product)
are not quite easy to install. You see, without AHCI you
cannot install the drivers as XP thinks it does not need them.
With AHCI, XP cannot access the drives, and if your board
is like mine, that means any drive. Pretty braindead.

What if you put the drivers on an IDE (PATA) drive or a USB drive?

 

[Daniel Prince]

Possibly. But you should not use mainboard RAID anyways. Better
use software RAID or get a separate RAID controller.

How much CPU time does a software RAID consume compared to an
inexpensive separate RAID controller? Or does it not really matter
if you have three or more CPU cores?

 

[Rod Speed]

Daniel Prince wrote

How much CPU time does a software RAID consume
compared to an inexpensive separate RAID controller?

**** all.

Or does it not really matter if you have three or more CPU cores?

Doesnt even matter with modern single core systems either.

The only time you get much cpu use is when replacing one of the drives etc.

 

[Rod Speed]

Daniel Prince wrote

What if you put the drivers on an IDE (PATA) drive

Doesnt help.

or a USB drive?

The problem is getting XP to load them from there.

 

[Bob Willard]

How much CPU time does a software RAID consume compared to an
inexpensive separate RAID controller? Or does it not really matter
if you have three or more CPU cores?
--

RAID0 and RAID1 are pretty light users of CPU time, until you
need to rebuild a RAIDset following a HD replacement. RAID5 does
require more computes during writes. So, I'd be willing to
user software RAID for RAID0/1, but I'd think seriously about
hardware for RAID5/6.

 

[Arno]

What if you put the drivers on an IDE (PATA) drive or a USB drive?

The driver files are not the problem. The OS is. If you put the
OS on an IDE or USB drive, yes, that works.

Arno

 

[Arno]

How much CPU time does a software RAID consume compared to an
inexpensive separate RAID controller? Or does it not really matter
if you have three or more CPU cores?

Inexpensive RAID controllers are FakeRAID (a.k.a. BIOS RAID)
and are software RAID anyways, just without the advantages.
And, yes, it does not matter, unless you are RAIDing SSDs.
The CPU overhead for HDDs is small (single digit percentages,
typically), unless you have a doubly degraded (2 drives missing)
RAID6.

Arno

 

[Arno]

RAID0 and RAID1 are pretty light users of CPU time, until you
need to rebuild a RAIDset following a HD replacement. RAID5 does
require more computes during writes. So, I'd be willing to
user software RAID for RAID0/1, but I'd think seriously about
hardware for RAID5/6.

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

 

[Bob Willard]

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.

 

[Arno]

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

 

[Rod Speed]

William R. Walsh wrote

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.

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.