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On Fri, 2015-12-04 at 07:46 -0500, Steve Pavlichek wrote:
RAID6 is a little slower due to 2 parity drives but better protection.
I usually recommend RAID5 with hot spare
You also have choices of Performance or Capacity option when starting RAID.
Performance option will give you 2 RAID sets and Capacity will give you 1
My gut feeling would be to go with raid6. With larger disks and the
statistical chance of a URE kicking a drive starting to fall within the
total amount of data needing to be read to re-build a set it makes more
sense. (Although statistically it may be small, and not evenly
distributed between multiple drives, confusing the issue further.)
My gut also says: if 8 drives are first turned on on the same day and
one fails then you can bet another will also fail as it has the same
life span/hours of use.
Added into all of that, if a raid set was 100% utilised the chances are
than on a normal yearly workload only 20% of that data might be accessed
regularly. Rebuilding a degraded raid set will hit 100% of all the disks
hammering the heads all over the place for many hours, touching that 80%
for the first time in years... if its going to fail, that would
definitely be the time another one of the disks decided to URE.
While raid/6 is slower, the question has to be: will the additional
overhead/reduction in write, and/or read, IO make a noticeable impact on
the workload thrown at it, or is a case of it being slower, but no one
would ever know unless the system were under spec'd with 100% disk
Here's a link to Sue Bakers parity set Techdoc
That's an interesting read. I'm guessing that with dual raid6 sets, its
similar to creating a raid/0 (stripe) over the top of two raid/6 sets.
I vaguely recall that the "400" (and possibly 36/38) didn't create
stripes or JBOD's (possibly multi-volume, fill disk1 first, then 2,
etc.) but instead used some form of "scatter gun" approach where it
spread the data across the devices, but did so in a non-uniform way
based on the data and not the disk layout. Mind you, when I heard/read
this it was years and years ago, so my understanding might not have been
From: Gad Miron
Sent: Friday, December 04, 2015 3:41 AM
Subject: Raid Configuration
To the Hardware guys
a quick one:
Due to replacing 3 SSDs installed for test puposes with (the original) 3
The BP is breaking the existing RAID5 set of 15 HDDs and is going to build
a 18 HDDs
RAID5 set (adding 3 HDDs)
My question, should we build istead a RAID6 set ?
what are the pros & cons?
This is a 8286 41A P8 machine with 18 283GB 15K discs all in the CEC
(plus 8 more in expansion 5887)
I believe that there is a EJ0P on-board controller .
So RAID5 or RAID6 ?
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