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.
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@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@kclug.org
>
[mailto:
kclug-bounces@kclug.org] On Behalf Of Luke-Jr
> Sent: Tuesday,
June 05, 2007 9:20 AM
> To: kclug@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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list
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