From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rudy Zijlstra Subject: Re: mdadm does not create partition devices whatsoever, "partitionable" functionality broken Date: Fri, 13 May 2011 22:00:07 +0200 Message-ID: <4DCD8DC7.1080707@grumpydevil.homelinux.org> References: <4DCD4A83.8060202@pulseforce.com> <4DCD6119.3080705@turmel.org> <4DCD67EF.1070602@pulseforce.com> <4DCD6B27.70402@pulseforce.com> <20110513234055.4307c536@natsu> <4DCD72AF.1070809@pulseforce.com> <4DCD75FE.8010703@turmel.org> <4DCD7E78.6050000@pulseforce.com> <4DCD800F.7080501@grumpydevil.homelinux.org> <4DCD8B32.9010901@pulseforce.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4DCD8B32.9010901@pulseforce.com> Sender: linux-raid-owner@vger.kernel.org To: Christopher White Cc: Roman Mamedov , Phil Turmel , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 05/13/2011 09:49 PM, Christopher White wrote: > On 5/13/11 9:01 PM, Rudy Zijlstra wrote: >> Hi Chris, >> >> >> I've run paritioned MD disks for several years now. I do that on >> systems where i use md for the system partitions. One mirror with >> partitions for the different system aspects. I prefer that, as it >> reflects best the actual physical configuration, and all partitions >> will be degraded at the same time when 1 disk develops a problem >> (which is unfortunately not the case when you partition the disk and >> then mirror the partitions). >> >> As i am a bit lazy and have only limited wish to fight with >> BIOS/bootloader conflicts / vagaries, these systems typically boot >> from the network (kernel gets loaded from the network, from there >> onwards all is on the local disk). >> >> Cheers, >> >> >> >> Rudy > Thank you for the information, Rudy, > > Your experience of running partitioned MD arrays for years shows that > it is indeed stable. The reason for wanting to skip LVM was that it's > one less performance-penalty layer, one less layer to configure, one > less possible point of failure, etc. I skip LVM cause for my usage pattern it only gives me an additional management layer... an additional layer to configure > > However, Phil again brings up the main fear that's been nagging me, > and that is that MD's partitioning support receives less love (use) > and therefore risks having bugs that go undiscovered for ages and > (gasp) may even risk corrupting the data. People are just so used to > LVM since MD used to be single-partition only, that > LVM+single-partition MD array is far more mature and far more in use. MD layer and LVM layer are independently maintained. There regular use together would trigger eventual bugs quicker though. > > My main reason against LVM was the performance penalty, where I had > read that it was in the 1-5% range, but I just did a new search and > saw threads showing that any performance hit claim is outdated and > that LVM2 is extremely efficient. In fact the CPU load didn't seem to > be impacted more than 0.1% or so in the graphs I saw. > > By the way, Rudy, as for your boot conflicts and the fact that you > resort to running a network boot, that was only a problem in the past > when bootloaders did not support software RAID. Grub2 supports GPT, MD > arrays with metadata 1.2, and can fully boot from a system (with > /boot) installation located on your MD array. All you'll have to do is > make sure your /boot partition (and the whole system if you want to) > is on a RAID 1 (mirrored) array, and that you install the Grub2 > bootloader on every physical disk. This means that it goes: > I know... but i happen to dislike grub2, and my network boot environment is stable and well maintained. Grub2 is for me a step backwards. more difficult to configure, and i've gone back to lilo as main bootloader.