On Mon, 26 Feb 2007, Neil Brown wrote: > On Sunday February 25, jpiszcz@xxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
