From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Turmel Subject: Re: RAID performance - new kernel results - 5x SSD RAID5 Date: Sat, 02 Mar 2013 12:07:07 -0500 Message-ID: <513231BB.4070903@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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5131C338.8010402@hardwarefreak.com> Sender: linux-raid-owner@vger.kernel.org To: stan@hardwarefreak.com Cc: Adam Goryachev , Linux RAID List-Id: linux-raid.ids 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. >> Is it worth reducing the chunk size from 64k down to 16k or even smaller? > > 64KB chunks should be fine here. Any gains with a smaller chunk would > be small, and would pale in comparison to the amount of PITA required to > redo the array and everything currently sitting atop it. Remember you'd > have to destroy it and start over. You can't change chunk size of an > existing array. Actually, you can. For levels 0 and 4,5,6. HTH, Phil