From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Dilger Date: Fri, 14 Sep 2001 09:52:31 -0600 Subject: Re: [linux-lvm] Re: =?unknown-8bit?B?W2xp?= =?unknown-8bit?Q?nux-lvm=5D_Verst=E4ndnis?= von Stripes bei LVM Message-ID: <20010914095230.S1541@turbolinux.com> References: <4C45858D148AD411A8B800A024B36E5009F4C994@granada.fhm.de> <20010914121333.A11814@dragon.blacknet.de> Mime-Version: 1.0 Content-Disposition: inline In-Reply-To: <20010914121333.A11814@dragon.blacknet.de> Sender: linux-lvm-admin@sistina.com Errors-To: linux-lvm-admin@sistina.com Reply-To: linux-lvm@sistina.com List-Help: List-Post: List-Subscribe: , List-Unsubscribe: , List-Archive: List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-lvm@sistina.com On Sep 14, 2001 12:13 +0200, Goetz Bock wrote: > On Fri, Sep 14 '01 at 11:32, Pawlowski Julian wrote: > > ich habe eine Frage zur Funktion von Stripes beim LVM. Wof?r genau > > ben?tigt man diese Funktion? Wird damit das LV auf mehrere der reellen > > Partitionen zwecks Performancegewinn verteilt? > > Yes, that's exactly the intended bahaviour. if you have n (e.g. 2 or > more) PV than a striped LV is splitted between this n PV. This can > increase performance (like RIAD0 does) but it may backfire, if your PV > are on the same reald device. > If you want to use striped LVs, only use one PV per real device. > > e.g.: 4 HDDs of 40GB each (sda, sdb, sdc, sdd) > > you boot from sda and decide to have a 512MB root/boot partition for > this. Than make 3 swap partitiones on sdb, sdc and sdd. > > on each device make a seccond partition with the rest of the space. > create a PV out of each of this 4 partitions. > > you now have: > > sda: sda1 512MB root/boot > sda2 39.5GB PV1 > sdb: sdb1 512MB swap > sdb2 39.5GB PV2 > sdc: sdc1 512MB swap > sdc2 39.5GB PV3 > sdd: sdd1 512MB swap > sdd2 39.5GB PV4 > > VG1: 118.0GB PV1 PV2 PV3 PV4 > > if you now make a striped LV of 20GB it will use 5GB on each PV and the > stripes will be read from PV1 PV2 PV3 PV4 PV1 PV2 PV3 PV4 ... A note here - very rarely can one really get the theoretical performance from striped LVs. There are several problems with stipes: - bus bandwidth is often limited, so you often do not get N*disk_bandwidth - application bandwidth is often limited, so you do not NEED N*disk_bandwidth - for EACH read from a striped LV, you need to seek all disks to that spot, which means you often have to wait for the MAXIMUM seek time of all disks. With non-striped LVs, you can do parallel read/write from different parts of the each disk (e.g. /usr, /home, /var, swap) - if you have problems with ANY disk, you have lost ALL of your data Cheers, Andreas -- Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto, \ would they cancel out, leaving him still hungry?" http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert