From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Turmel Subject: Re: RAID performance - new kernel results - 5x SSD RAID5 Date: Sun, 03 Mar 2013 20:31:06 -0500 Message-ID: <5133F95A.5040508@turmel.org> References: <51134E43.7090508@websitemanagers.com.au> <51137FB8.6060003@websitemanagers.com.au> <5113A2D6.20104@websitemanagers.com.au> <51150475.2020803@websitemanagers.com.au> <5120A84E.4020702@websitemanagers.com.au> <51222A81.9080600@hardwarefreak.com> <51250377.509@websitemanagers.com.au> <5125B8E5.5000502@hardwarefreak.com> <5125C154.3090603@websitemanagers.com.au> <51272808.7070302@hardwarefreak.com> <512A79D3.9020502@hardwarefreak.com> <5130D206.4090302@websitemanagers.com.au> <5131C338.8010402@hardwarefreak.com> <513231BB.4070903@turmel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Adam Goryachev Cc: stan@hardwarefreak.com, Linux RAID List-Id: linux-raid.ids On 03/03/2013 10:19 AM, Adam Goryachev wrote: > Phil Turmel wrote: > >> On 03/02/2013 04:15 AM, Stan Hoeppner wrote: >>> On 3/1/2013 10:06 AM, Adam Goryachev wrote: >> >>>> 15) "Make sure all LVs are aligned to the underlying md device >>>> geometry. This will eliminate any possible alignment issues." >>>> What does this mean? The drive partitions are now aligned properly, >>>> but how does LVM allocate the blocks for each LV, and how do I >>>> ensure it does so optimally? How do I even check this? >>> >>> I'm not an LVM user so I can't give you command lines. But what I >>> can tell you follows, and it is somewhat critical to RMW performance, >>> more for rust but also for SSD to a lesser degree. >> Run "dmsetup table" and look at the start sectors for your volumes: >> Fast-Root: 0 314572800 linear 9:3 3072 >> This volume starts at sector 3072 (1.5MB) on /dev/sda3. So the volume >> alignment within LVM is 512K. > > I see this (for the first LV) > vg0-hostname: 0 204808192 linear 147:2 512 > So, I'm guessing mine is starting at 512, and is also aligned at 512k ? Not quite. Those size and offset numbers are shown in *sectors*, so you have 256k alignment. But that's exactly the minimum you need to match your raid5 chunk size, so you are good for the moment. > Also, pvdisplay tells me the PE Size is 4M, so I'm assuming that regardless of how the LV's are arranged, they will always be 512k aligned? 256k, but yeah. > So, is that enough to be sure that this is not an issue? It looks to me like you are good on alignment. Phil