[NBLUG/talk] RAID?

Scrappy Laptop scrappylaptop at yahoo.com
Mon Dec 31 10:03:46 PST 2007


  Most onboard RAID controllers are very similar to Winmodems; the actual calculations are offloaded to the system CPU via drivers, which not only means that the CPU is tied up but also the main memory bus and PCI bus, which precludes use by other processes and imparts a  task-switching cost.  A true hardware RAID chip, on the other hand, handles the parity and striping calculations onboard; the only information travelling on the main system bus (i.e., PCI) is the application data being read or written.

  Software RAID is usually the way to go in my opinion, unless you have a new, good quality, full hardware RAID board with a large amount of onboard cache memory.  Google "Linux RAID software hardware performance" (no quotes) and you'll find many benchmarks that show that using software RAID gives higher performance than either older hardware raid boards or the 'WinRAID' type chips (originally nicknamed after the Promise IDE-133 add on boards, I believe).  Unless the cost can be justified for a good hardware RAID, I like to use software raid because it is trivial to adjust settings such as stripe and buffer sizes.  A half hour of tinkering with them can result in large performance gains, especially on servers that use a set size for pages or blocks of data, such as a SQL server.  

  One final consideration is that *any* Linux system with correct cable (i.e., SATA or PATA) and the correct packages installed can remount a software RAID volume;  if you go with hardware RAID, you potentially need the same make and model of card to read the drives should a failure occur.  That can be a big consideration, depending on your backup strategies.

  I came across a basic Logical Volume Management tutorial that includes a vmware image as a learning aide.  It's a nice easy way to learn about volume management and RAID, as the the tutorial is able to reference a predetermined environment as it walks you through the various exercises and you can freeze the system state as needed: http://www.howtoforge.com/linux_lvm

-Frank

Kyle Rankin <kyle at nblug.org> wrote: On Mon, Dec 31, 2007 at 11:35:38AM -0500, Jack Smith wrote:
> OK, I'm ready to start setting up RAID in Fedora 8.
> 
> "The motherboard comes with the Silicon Image Sil3 1 3 2 and the NVIDIA
> nForce 4 SLI Southbridge RAID controllers that allow you to configure Serial
> ATA hard disk drives as RAID sets."
> 
> Does this mean hardware RAID is supported?  Where do I start looking to set
> it up?
> 
> Thanks,
> -- 
> Jack Smith
> 
> English doesn't borrow from other languages -- English follows other
> languages down dark alleys and takes what it wants.


Most of the on-board RAID you will see in consumer motherboards aren't
actual "hardware" RAID because they require the OS to have driver support
to see the array. In my opinion it's better to use Linux software RAID as
it's more stable, has more features, and you can migrate to new hardware
much more easily.

-- 
Kyle Rankin
NBLUG President
The North Bay Linux Users Group
http://nblug.org
IRC: greenfly at irc.freenode.net #nblug 
kyle at nblug.org

_______________________________________________
talk mailing list
talk at nblug.org
http://nblug.org/cgi-bin/mailman/listinfo/talk


       
---------------------------------
Looking for last minute shopping deals?  Find them fast with Yahoo! Search.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://nblug.org/pipermail/talk/attachments/20071231/bb06efc5/attachment.htm 


More information about the talk mailing list