Message-ID: <4E546FCB.2050703@2ndQuadrant.com>
Date: Tue, 23 Aug 2011 23:28:11 -0400
From: Greg Smith <greg@2ndQuadrant.com>
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To: pgsql-performance@postgresql.org
Subject: Re: RAID Controllers
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On 08/23/2011 06:42 PM, David Boreham wrote:
> I took a look at Areca. The fan on the controller board is a big
> warning signal for me (those fans are in my experience the single most
> unreliable component ever used in computers).

I have one of their really early/cheap models here, purchased in early 
2007 .  The fan on it just died last month.  Since this is my home 
system, I just got a replacement at Radio Shack and spliced the right 
connector onto it; had it been a production server I would have bought a 
spare fan with the system.

To put this into perspective, that system is on its 3rd power supply, 
and has gone through at least 4 drive failures since installation.

> Can you say a bit more about the likely problems with the CLI ?

Let's see...this week I needed to figure out how to turn off the 
individual drive caches on a LSI system, they are set at the factory to 
"use disk's default" which is really strange--leaves me not even sure 
what state that is.  The magic incantation for that one was:

MegaCli -LDSetProp DisDskCache -LALL -aALL

There's a certainly a learning curve there.

> I'm thinking that I configure the card once, and copy the config
> to all the other boxes, so even if it's as obscure as Cisco IOS,
> how bad can it be ? Is the concern more with things like a rebuild;
> monitoring for drive failures -- that kind of constant management
> task ?

You can't just copy the configurations around.  All you have are these 
low-level things that fix individual settings.  To get the same 
configuration on multiple systems, you need to script all of the 
changes, and hope that all of the systems ship with the same defaults.

What I do is dump the entire configuration and review that carefully for 
each deployment.  It helps to have a checklist and patience.

> How about Adaptec on Linux ? The supercapacitor and NAND
> flash idea looks like a good one, provided the firmware doesn't
> have bugs (true with any write back controller though).

I only have one server with a recent Adaptec controller, a 5405.  That 
seemed to be the generation of cards where Adaptec got their act 
together on Linux again, they benchmarked well in reviews and the 
drivers seem reasonable.  It's worked fine for the small server it's 
deployed in.  I haven't been able to test a larger array with one of 
them yet, but it sounds like you're not planning to run one of those 
anyway.  If I had 24 drives to connect, I'd prefer an LSI controller 
just because I know those scale fine to that level; I'm not sure how 
well Adaptec does there.  Haven't found anyone brave enough to try that 
test yet.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us