From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: mdadm raid1 read performance Date: Thu, 05 May 2011 09:26:45 +0200 Message-ID: References: <20110504105822.21e23bc3@notabene.brown> <4DC0F2B6.9050708@fnarfbargle.com> <20110505094538.0cef02cc@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 05/05/2011 02:40, Liam Kurmos wrote: > Cheers Roberto, > > I've got the gist of the far layout from looking at wikipedia. There > is some clever stuff going on that i had never considered. > i'm going for f2 for my system drive. > > Liam > For general use, raid10,f2 is often the best choice. The only disadvantage is if you have applications that make a lot of synchronised writes, as writes take longer (everything must be written twice, and because the data is spread out there is more head movement). For most writes this doesn't matter - the OS caches the writes, and the app continues on its way, so the writes are done when the disks are not otherwise used. But if you have synchronous writes, so that the app will wait for the write to complete, it will be slower (compared to raid10,n2 or raid10,o2). The other problem with raid10 layout is booting - bootloaders don't much like it. The very latest version of grub, IIRC, can boot from raid10 - but it can be awkward. There are lots of how-tos around the web for booting when you have raid, but by far the easiest is to divide your disks into partitions: sdX1 = 1GB sdX2 = xGB sdX3 = yGB Put all your sdX1 partitions together as raid1 with metadata layout 0.90, format as ext3 and use it as /boot. Any bootloader will work fine with that (don't forget to install grub on each disk's MBR). Put your sdX2 partitions together as raid10,f2 for swap. Put the sdX3 partitions together as raid10,f2 for everything else. The most flexible choice is to use LVM here and make logical partitions for /, /home, /usr, etc. But you can also partition up the md device in distinct fixed partitions for /, /home, etc. if you want. Don't try and make sdX3 and sdX4 groups and raids for separate / and /home (unless you want to use different raid levels for these two groups). Your disks are faster near the start (at the outer edge of the disk), so you get the best speed by making the raid10,f2 from almost the whole disk. mvh., David