[conspire] (forw) Re: SATA and Linux Raid on a Intel Desktop 945 board

[Rick Moen]

----- Forwarded message from Andrew Jones <andrew-jones at lineone.net> -----

From: [snip]
To: rick at linuxmafia.com
Date: Sat, 26 Nov 2005 09:28:51 -0000
Organization: Personal Email
X-Mailer: Microsoft Office Outlook, Build 11.0.6353
Subject: SATA and Linux Raid on a Intel Desktop 945 board

Hi Rick, 
 

We are looking to use an Intel 945 Desktop board with SATA drives and RAID 1
and 5. 

 

Just wondered what you would recommend in order to provide the RAID. It
appears that the RAID on board is not real raid and so if we need to go to a
card what would you recommend on the following points. 

 

1.	Most reliable under Linux
2.	Best supported in the Linux source community 

 

Regards,
[snip]


----- End forwarded message -----
----- Forwarded message from Rick Moen <rick at linuxmafia.com> -----

Date: Mon, 28 Nov 2005 19:57:43 -0800
From: Rick Moen <rick at linuxmafia.com>
To: [snip]
Subject: Re: SATA and Linux Raid on a Intel Desktop 945 board

Quoting [address snipped]:

> Hi Rick, 

Hi, Andrew.  I'm on about 3 1/2 hours of sleep, and barely coherent.

> We are looking to use an Intel 945 Desktop board with SATA drives and
> RAID 1 and 5. 

OK.  You probably are aware that the Intel SATA chipset (the i945
motherboard's South Bridge) in question is ICH7.  (You _could_ have
saved me 20 seconds of research time, if you did.  ;->  )

All I know about Linux support for ICH7 is on
http://linuxmafia.com/faq/Hardware/sata.html#ich7 and referenced entries
about ICH5, ICH6, and AHCI.

> Just wondered what you would recommend in order to provide the RAID.
> It appears that the RAID on board is not real raid and so if we need
> to go to a card what would you recommend on the following points. 
> 
> 1.	Most reliable under Linux
> 2.	Best supported in the Linux source community 

Your first question is:  real hardware RAID, fakeraid, or Linux's
own software RAID ("md" driver)?  I shouldn't make it sound as if I'm
sneering about any of those, since I'm not.  Each has its merits.  If
you read through my above-referenced page, you'll get part of that.


Real hardware RAID:   Good:  Unparalleled performance and reliability.
Basically completely eliminates and entire category of software
problems, in that whatever array you set up is defined and operated 
entirely in hardware, and is software-transparent.  Bad:  Costs money.
Many hardware RAID controllers lack Linux-native management software,
so you might end up having to do such functions via the card's
BIOS-based administrative interface, during host downtime.  If the
card fails, you have to buy another one just like it to ransom your RAID
set back, or else give up and restore from backup.

Fakeraid:  Good:  It's not only cheap, but pretty much thrown in for 
free on modern motherboards (e.g., Intel ICH* or Silicon Image).  CPU
loading typically doesn't matter except during restriping/rebuild
operations, because typical Linux boxes' CPUs are severely underused.
Bad:  Often need to have a very, very recent Linux installer kernel to 
properly support the continually changing flow of new fakeraid chipsets
into the market.  If the card (or motherboard with integrated fakeraid
SATA) fails, you have to buy another one just like it to ransom your
RAID set back, or else give up and restore from backup.  Most have
no provision for hotswapping/hot-sparing.  And you'll _definitely_ be
doing array administration from the card's firmware interface (involving
downtime).

Linux software RAID:  Good:  Price can't be beat.  Works on any hardware
at all.  Can do all RAID levels of interest.  RAID sets can be moved to 
any replacement hardware whatsoever if a host adapter fails:  You don't
need to buy another of anything.  Bad:  Significantly complicates your
setup, especially booting.  (You'll want to read some docs about that, 
and I'm pretty sure your boot code won't be able to live on a RAID5
volume.)  As with fakeraid, slight CPU loading, especially during
restriping/rebuild operations.


Which way should you go?  Beats me.  Personally, I like to usde slightly
trailing-edge hardware, specifically so that people like you will get
the bugs out for me.  ;->  Besides, I'm cheap.  And I prefer to use
completely hassle-free hardware so that if I end up enduring software
hassles, I'm not driven out of my mind.  (I'm not willing to be hassled
simultaneously by both hardware and software problems.)

One thing's for certain:  If using ICH7 (or any other recent-release
fakeraid chipset), you'll be limited to Linux distribution installers 
with very cutting-edge installation kernels, preferably 2.6.x .

If you want opinions from people who actually have been in the current 
market for Linux hardware, and who aren't deliberately letting other
pioneers be the ones getting arrows in their backs, you might want to 
ask on Usenet's comp.os.linux.hardware newsgroup.

And by the way:  You should really ideally be posting your query to 
places like that, rather than my mailbox -- but I'm sending this lengthy
response in order to forward both mails to my user group.  ;->

-- 
Cheers,             
Rick Moen                 "Anger makes dull men witty, but it keeps them poor."
rick at linuxmafia.com                                   -- Elizabeth Tudor

----- End forwarded message -----