From owner-freebsd-scsi@FreeBSD.ORG Sat Nov 26 20:07:06 2005 Return-Path: X-Original-To: freebsd-scsi@freebsd.org Delivered-To: freebsd-scsi@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id BA0B716A41F for ; Sat, 26 Nov 2005 20:07:06 +0000 (GMT) (envelope-from user@dhp.com) Received: from shell.dhp.com (shell.dhp.com [199.245.105.1]) by mx1.FreeBSD.org (Postfix) with ESMTP id 4720343D5A for ; Sat, 26 Nov 2005 20:07:04 +0000 (GMT) (envelope-from user@dhp.com) Received: by shell.dhp.com (Postfix, from userid 896) id EB4C231373; Sat, 26 Nov 2005 15:07:02 -0500 (EST) Date: Sat, 26 Nov 2005 15:07:02 -0500 (EST) From: user To: Herve Boulouis In-Reply-To: <20051126194152.GA594@ra.aabs> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=X-UNKNOWN Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: freebsd-scsi@freebsd.org Subject: Re: configuration choices with Dell CERC (adaptec 2610SA) X-BeenThere: freebsd-scsi@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SCSI subsystem List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 26 Nov 2005 20:07:06 -0000 On Sat, 26 Nov 2005, Herve Boulouis wrote: > Le 26/11/2005 14:17, user a =E9crit: > >=20 > > Read caching: yes/no (default is yes) > >=20 > > (read caching does not rely on a battery, and is completely "safe", > > right? I am going to set this to "yes", however I wonder - why would > > anyone _ever_ set it to "no" ?) > =20 > You usually want to disable read caching on all aac based adaptec raid > controllers because it decreases performance. Thanks - I did not know that, and that is good to know. > > Write caching: enable/disable > > > > (this is the one that can get you into trouble if the system loses powe= r > > before a write is committed to disk, and the battery is dead, right? I= am > > going to set this to "disable" because I do not think the 2610SA has a > > battery ... right ?) >=20 > If your server is plugged on a UPS you can safely enable it, it's quite > a performance gain. Ok. It is. However, my experience has been that no matter how rock solid the datacenter provided, UPS backed power is, there is a power interruption about every 1-2 years (and this experience comes from very very good datacenters - from Level3 to UUnet, etc.) ... so ... let's say I bank on this and enable write caching, how big of a deal is it when that power interruption does come ? Assuming freebsd 6.0 and UFS2 ... is it just an fsck, or is there a potential for some real problems if the kernel thinks something is totally committed, but it never makes it to the drive ? > > Rebuild rate: high/medium/low > >=20 > > (I have no idea what this means - I never saw this in adaptec bios befo= re > > ... can anyone define exactly what this means ?) >=20 > This controls how much ressources the card will put in rebuilding a volum= e > that got a failed disk. A high rebuild rate will mean a short rebuild tim= e > but slower disk accesses during the rebuild. I am going to set it to "low" then ... my experience is that a failed disk often rebuilds itself only to re-fail shortly thereafter, thus making possible a continuous loop of rebuilding over and over ... which would essentially take the system offline if all resources were dedicated to the rebuild. Comments ? thanks very much.