From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roy Sigurd Karlsbakk Subject: Re: recommended way to add ssd cache to mdraid array Date: Sat, 12 Jan 2013 17:37:09 +0100 (CET) Message-ID: <9897176.12.1358008628959.JavaMail.root@zimbra> References: <50F16FAC.7000509@hardwarefreak.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <50F16FAC.7000509@hardwarefreak.com> Sender: linux-raid-owner@vger.kernel.org To: stan@hardwarefreak.com Cc: Chris Murphy , linux-raid Raid List-Id: linux-raid.ids > > uh=E2=80=A6 how can the filesystem chosen be relevant to the disk e= levator? >=20 > It's the other way round. The chosen elevator can cause problems with > the filesystem. You should find this relevant conversation amongst th= e > lead XFS developers educational: >=20 > http://oss.sgi.com/archives/xfs/2011-07/msg00464.html This article is about using CFQ with RAID controllers with write cache,= which isn't something I'd recommend. CFQ is, if I'm not mistaken, good= if Linux has local access to each disk, and the disks are spinning (!S= SD). > > CFQ will try to optimize access to reduce seeks >=20 > "Completely Fair Queuing" -- The name alone tells you how it works. I= t > most certainly does not do what you state. Please read the brief > Wikipedia article: http://en.wikipedia.org/wiki/CFQ It's how it's designed, for spinning rust. > > and should be completely independent on the filesystem used on top. >=20 > Operative word: "should" >=20 > The USA should not be $16 Trillion in debt, but it is. By > international > law whales should not be killed, but they still are. Etc. Well, most things don't work as they are intended to do, but I guess CF= Q works pretty well for spinning rust directly attached to a Linux box. The default scheduler was changed in kernel, but only because SSDs are = getting more common. Would those kernel developers know their things? Vennlige hilsener / Best regards roy -- Roy Sigurd Karlsbakk (+47) 98013356 roy@karlsbakk.net http://blogg.karlsbakk.net/ GPG Public key: http://karlsbakk.net/roysigurdkarlsbakk.pubkey.txt -- I all pedagogikk er det essensielt at pensum presenteres intelligibelt.= Det er et element=C3=A6rt imperativ for alle pedagoger =C3=A5 unng=C3=A5= eksessiv anvendelse av idiomer med xenotyp etymologi. I de fleste tilf= eller eksisterer adekvate og relevante synonymer p=C3=A5 norsk. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html