Re: SSDs - RAID or Mirror ?

Mirror will nearly always outperform RAID.
Mirror is always two writes for a write, one read (with two choices) for a
read.
RAID 5 is two reads and two writes for a write, one read (with one choice)
for a read.

SSDs are so fast you can do mirroring on some of the lower cost
controllers with NO Cache. In fact some are SSD only.

I can't put my finger on it just now but Sue Baker has frequently
indicated Mirror over RAID as well for SSDs.

- Larry "DrFranken" Bolhuis

www.frankeni.com
www.iDevCloud.com
www.iInTheCloud.com

On 10/15/2014 7:53 PM, Evan Harris wrote:

Hi Larry

that's what I have done in the past and that is my preference. Is there an
IBM best practise recommendation I can refer to or do that you know of or
do you have some logic as to why (like, because they are SSD's)

I'm guessing you have something due to the quick answer.. :)

On Thu, Oct 16, 2014 at 12:29 PM, DrFranken <midrange@xxxxxxxxxxxx>
wrote:

Mirror. Done.

- Larry "DrFranken" Bolhuis

www.frankeni.com
www.iDevCloud.com
www.iInTheCloud.com


On 10/15/2014 7:01 PM, Evan Harris wrote:

Hi all

I have a customer who has a ordered a system with 4 x 387Gb SSDs in the
CEC
and 24 x 283Gb disks housed in a 5887.

With respect to the SSDs, what is the better approach - Mirroring or
RAID
? The system is not pushed for space so mirroring is an option if there
is
a reason for doing that, otherwise either approach works fine for this
install.

I normally prefer to hot spare RAID sets these days and I guess I could
do
a 3 disk RAID set and hot spare it (not my preference...) but in that
case
it seems to me MIrroring would probably be a better approach.

Any opinions as to which approach is better ?


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