Re: Rép. : Question of a Newbie to POWER Systems

True the math does work out better, but....

It still winds up being effectively three drives, and worse yet from a write perspective, mirrored. A write to 3 mirrored pairs has to wait for both of the drives in the mirrored pair to commit the write before it is released by the storage subsystem to the OS. If you get a large write that affects more than one of the mirrored pairs, you now have to wait on all four, or possibly all six drives to complete the write operation.

Read is some what quicker since it can come from either drive in the mirrored set.

Since the original question was regarding disk performance a three drive system (or three mirrored pairs) without much write cache, the system is going to have problems with any moderate level of I/O.

Jim Oberholtzer
CEO/Chief Technical Architect
Agile Technology Architects, LLC


On 3/29/2011 1:08 PM, Porterfield, Sean wrote:

That math does work out better!
--
Sean Porterfield


-----Original Message-----
From: John Jones
Sent: Monday, March 28, 2011 13:35
To: Midrange Systems Technical Discussion
Subject: Re: Rép. : Question of a Newbie to POWER Systems

Since the OP said

"It contains 3 disks of 140 GB - Which are RAID-1 mirrored totalling 420GB effective."

I was assuming it was 3 pairs/6 physical units.


On Mon, Mar 28, 2011 at 11:49 AM, Porterfield, Sean

> Since he said RAID1-mirrored, I think it's really 4 drives rather than 3.
> If not, that would be the first thing to fix, because a disk is
> unprotected.
> --
> Sean Porterfield
>
>
> --

JJ
4 Out of 3 people have trouble with fractions.