From mboxrd@z Thu Jan 1 00:00:00 1970 From: "K. Richard Pixley" Subject: Confused by performance Date: Wed, 16 Jun 2010 11:08:48 -0700 Message-ID: <4C191330.5060905@noir.com> References: <4BFAEABD.2070700@noir.com> <4BFF2024.3040509@noir.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed To: linux-btrfs@vger.kernel.org Return-path: In-Reply-To: <4BFF2024.3040509@noir.com> List-ID: Once again I'm stumped by some performance numbers and hoping for some insight. Using an 8-core server, building in parallel, I'm building some code. Using ext2 over a 5-way, (5 disk), lvm partition, I can build that code in 35 minutes. Tests with dd on the raw disk and lvm partitions show me that I'm getting near linear improvement from the raw stripe, even with dd runs exceeding 10G, so I think that convinces me that my disks and controller subsystem are capable of operating in parallel and in concert. hdparm -t numbers seem to support what I'm seeing from dd. Running the same build, same parallelism, over a btrfs (defaults) partition on a single drive, I'm seeing very consistent build times around an hour, which is reasonable. I get a little under an hour on ext4 single disk, again, very consistently. However, if I build a btrfs file system across the 5 disks, my build times decline to around 1.5 - 2hrs, although there's about a 30min variation between different runs. If I build a btrfs file system across the 5-way lvm stripe, I get even worse performance at around 2.5hrs per build, with about a 45min variation between runs. I can't explain these last two results. Any theories? --rich