From mboxrd@z Thu Jan 1 00:00:00 1970 From: Justin Piszcz Subject: Re: Linux Software RAID Bitmap Question Date: Wed, 28 Feb 2007 14:44:23 -0500 (EST) Message-ID: References: <17890.24681.249414.635536@notabene.brown> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: dean gaudet Cc: Neil Brown , linux-raid@vger.kernel.org, Alan Piszcz List-Id: linux-raid.ids On Wed, 28 Feb 2007, dean gaudet wrote: > On Mon, 26 Feb 2007, Neil Brown wrote: > >> On Sunday February 25, jpiszcz@lucidpixels.com wrote: >>> I believe Neil stated that using bitmaps does incur a 10% performance >>> penalty. If one's box never (or rarely) crashes, is a bitmap needed? >> >> I think I said it "can" incur such a penalty. The actual cost is very >> dependant on work-load. > > i did a crude benchmark recently... to get some data for a common setup > i use (external journals and bitmaps on raid1, xfs fs on raid5). > > emphasis on "crude": > > time sh -c 'tar xf /var/tmp/linux-2.6.20.tar; sync' > > xfs journal raid5 bitmap times > internal none 0.18s user 2.14s system 2% cpu 1:27.95 total > internal internal 0.16s user 2.16s system 1% cpu 2:01.12 total > raid1 none 0.07s user 2.02s system 2% cpu 1:20.62 total > raid1 internal 0.14s user 2.01s system 1% cpu 1:55.18 total > raid1 raid1 0.14s user 2.03s system 2% cpu 1:20.61 total > > > raid5: > - 4x seagate 7200.10 400GB on marvell MV88SX6081 > - mdadm --create --level=5 --raid-devices=4 /dev/md4 /dev/sd[abcd]1 > > raid1: > - 2x maxtor 6Y200P0 on 3ware 7504 > - two 128MiB partitions starting at cyl 1 > - mdadm --create --level=1 --raid-disks=2 --auto=yes --assume-clean /dev/md1 /dev/sd[fg]1 > - mdadm --create --level=1 --raid-disks=2 --auto=yes --assume-clean /dev/md2 /dev/sd[fg]2 > - md1 is used for external xfs journal > - md2 has an ext3 filesystem for the external md4 bitmap > > xfs: > - mkfs.xfs issued before each run using the defaults (aside from -l logdev=/dev/md1) > - mount -o noatime,nodiratime[,logdev=/dev/md1] > > system: > - dual opteron 848 (2.2ghz), 8GiB ddr 266 > - tyan s2882 > - 2.6.20 > > -dean > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > I like your crude benchmark, it works well. I have not tested with a bitmap, but it does not seem worth it to use those. Here are my results (for disk speed/purposes only): All FS are XFS with similar mount options as yours. Raid1 Dual 74GB Raptor (older models, no NCQ) [no bitmap] # time sh -c 'tar xf linux-2.6.20.tar; sync' real 0m40.226s user 0m0.200s sys 0m1.515s Raid5 Quad 150 Raptor (NCQ) [no bitmap] # time sh -c 'tar xf linux-2.6.20.tar; sync' real 0m21.721s user 0m0.174s sys 0m1.541s Raid5 Six 400GB Sata Drives (some NCQ, some not) [no bitmap] # time sh -c 'tar xf linux-2.6.20.tar; sync' real 1m7.322s user 0m0.194s sys 0m1.492s