Torrey Hoffman wrote: > > I've been putting together a new workstation, and in the process of > building and testing it I ran into an odd performance anomaly. It > probably only matters for people benchmarking different reiserfs > setups, but I'd like to know what causes it. > > In short: If you make a new reiserfs partition, immediately mount it, > and run benchmarks, it is noticeably slower than the exact same > partition after a reboot and remount. There can be as much as a > 25 % speed increase just from rebooting! > > I've seen this repeatedly on both single disks and a variety of RAID > setups. Details of my setup and some of the testing I've done are below. > > Note that mkreiserfs warns that rebooting after fdisk is required. > I haven't been using fdisk at all - I am running mkreiserfs on raw > drives and raid devices with no partition tables. > > Perhaps the warning should be that a reboot is required after > running mkreiserfs? > > Anyway, some details: > > My computer setup: > - Dual P3 800 (133Mhz) Tyan Tiger MB with VIA chipset, 512 MB RAM > - Linux 2.4.9-ac17, no other patches. > - Distribution is approximately Mandrake 8.1 (8.0 + most of Cooker) > - all benchmark numbers are based on three consecutive runs of > "dbench -c ../client.txt 32", reporting the "Throughput" numbers. > > - All testing was done with no X running - just basic system daemons > - System runs from /dev/hda which is an IBM 7200 RPM drive using the > onboard VIA IDE controller. > > - /dev/hd[e,f,g,h] are four 60 GB 5400 RPM Maxtor drives on a Promise > Ultra TX2-100, two drives per cable, ATA 100. > - init scripts do "hdparm -c1 -d1 -m16 -W1 -A1" for all hard drives > > Raw device speed: > hdparm -t -T /dev/hde : buffer-cache 182 MB/s, disk = 27.7 MB/s > > Testing on a single disk, /dev/hde, no partition table > - mkreiserfs /dev/hde, mount, 3 runs of dbench 32 = 36 - 44 > MB/s > - after reboot, mount, 3 runs of dbench 32 = 52 - 56 > MB/s > > raid 0 with two IDE masters only (/dev/hde & /dev/hdg), chunk size 2048 > - mkraid, mkreiserfs /dev/md0, mount, 3 runs of dbench 32 = 52 - 57 > MB/s > - after reboot, mount /dev/md0, 3 runs of dbench 32 = 68 - 69 > MB/s > > After those tests I always rebooted. > > raid 0 - all four Maxtors, chunk size 2048 > - mkraid, mkreiserfs, reboot, mount, 3 dbench runs = 71 - 73 > MB/s > > raid 0 - all four Maxtors, chunk size 1024 > - mkraid, mkreiserfs, reboot, mount, 3 dbench runs = 72 - 74 > MB/s > > This machine will eventually have 1 GB of RAM, two Promise Ultra TX2 100 > controllers with one Maxtor drive per cable, and will be running in a RAID 5 > > configuration. For now I'm just experimenting to check speed and stability. > > Torrey Hoffman Would results be explained by full write cache creating IO demands on subsequent running of benchmark?
Hans
