SATA PT2

[Phil Thayer]

True.  I missed that on the RAID 0 as opposed to RAID 1.
 
Also, you would probable be surprised at the number of places that use
the RAID 6 or RAID ADG in a mirrored configuration.  It is not a fast or
speedy  solution.  Remember that RAID 6 or RAID ADG is the SLOWEST RAID
as far as performance is concerned.  With RAID 10 you still open
yourself up to vulnerability when a drive fails on your stripeset which
causes your stripeset to fail.  Since it is mirrored you are fine unless
you have a failure on your mirrored stripeset.  Personally, I don't like
to use RAID 0 at anytime because it has no resiliency when it comes to
disk failures.  I would rather have the RAID 5 at a minimum for any
single disk LUN and then use RAID 1 for additional redundancy.  But
generally I work with companies that are willing to spend the money for
that configuration along with having controllers with the maximum
read/write cache to compensate for the speed.
 


________________________________

	From: Jeremy Fowler [mailto:jeremy.f76 at gmail.com] 
	Sent: Tuesday, June 05, 2007 2:17 PM
	To: Phil Thayer
	Cc: kclug at kclug.org
	Subject: Re: SATA PT2
	
	
	RAID 0 is a striped set, no parity.
	RAID 1 is a mirrored set.
	
	So RAID60 would be two RAID 6 arrays striped together.
	
	RAID61 would be two mirrored RAID 6 arrays... I could see maybe
why you would strip two RAID 6 arrays to increase performance, but that
would be incredibly costly and I would say complete overkill.  If you
need redundancy and speed is a high priority, you might as well do
RAID10, a stripped set of mirrored drives. However, if you a have a
limited number of drives and needed the most storage size by reducing
the ratio of parity drives and disk I/O performance isn't too important
then RAID 5/6 is your answer. 
	
	
	On 6/5/07, Phil Thayer <phil.thayer at vitalsite.com> wrote: 

		If you do that you need to make sure that the controller
will support
		RAID 6 or RAID ADG.  This is simply a RAID 5 with an
additional parity
		disk implemented.  This reduces the risk of failure of
the entire RAID
		if a single disk fails.  The RAID will simply function
as if it were a
		RAID 5 until the failed disk is physically replaced and
the RAID 6 or
		RAID ADG is rebuilt.
		
		As an alternative, if you have a controller that does
not have RAID 6 or 
		RAID ADG, then you can use RAID 5 with a spare disk set
aside for use as
		a spareset in case of a failure.  This does not
eliminate the risk in
		case of a single disk failure but it reduces it to the
time required to 
		rebuild the RAID using the spareset as opposed to the
time it takes to
		physically replace a drive in a degraded RAID 5. If you
suffer a second
		disk drive failure during the time that the RAID 5 is
rebuilding after 
		the first disk drive failure, then you will loose your
entire RAID.
		
		The ultimate high availability configuration would be
RAID 60+.  This
		would be two RAID 6 with their own sparesets assigned,
mirrored to each 
		other.  However, be prepared to loose a larger
percentage of your raw
		disk drive space.  You will loose the equivalent of:
		
		Two disk drives for each RAID 6 used
		Two disk drives for each RAID 6 for redundant sparesets 
		One raid 6 with the mirroring
		
		I really don't expect that you would build something
like that for a
		home server but I figured I would throw all that out
there just in case
		you had more money that you know what to do with and
want to make sure 
		the data on your server is safe from failure.
		
		Phil
		
		> -----Original Message-----
		> From: kclug-bounces at kclug.org
		> [mailto: kclug-bounces at kclug.org
<mailto:kclug-bounces at kclug.org> ] On Behalf Of Luke-Jr
		> Sent: Tuesday, June 05, 2007 9:20 AM
		> To: kclug at kclug.org
		> Subject: Re: SATA PT2
		>
		> On Tuesday 05 June 2007 09:11, Phil Thayer wrote: 
		> > Not to mention that with the recent SATA drive sizes
to get
		> 1TB of SATA
		> > would only take 2 drive.  However, if you want to
use a
		> multi-channel
		> > SATA controller with raid you will want to use
smaller 
		> drives (like 4 x
		> > 300 or 8 X 250) so you don't loose too much capacity
to parity.
		>
		> With 8 drives, I'd probably want to make 2 parity for
a
		> server... As unlikely
		> as it is for 2 drives to fail at once, that chance
does 
		> increase with # of
		> drives.
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