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From: Arno on 5 Apr 2010 20:56
Daniel Prince <neutrino1(a)ca.rr.com> wrote:
> Arno <me(a)privacy.net> wrote:

>>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?

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 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: Arno on 5 Apr 2010 20:59
Daniel Prince <neutrino1(a)ca.rr.com> wrote:
> Arno <me(a)privacy.net> wrote:

>>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?

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 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: Arno on 5 Apr 2010 21:06
Bob Willard <BobwBSGS(a)trashthis.comcast.net> wrote:
> Daniel Prince wrote:
>> Arno <me(a)privacy.net> wrote:
>>
>>> 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?
>> --

> 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
--
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: Bob Willard on 6 Apr 2010 05:50
Arno wrote:
> Bob Willard <BobwBSGS(a)trashthis.comcast.net> wrote:
>> Daniel Prince wrote:
>>> Arno <me(a)privacy.net> wrote:
>>>
>>>> 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?
>>> --
>
>> 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

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.
--
Cheers, Bob
From: William R. Walsh on 6 Apr 2010 14:50
Hi!

> 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 -- 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.

William


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