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Re: [nslu2-linux] SLUG performance report

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  • Shane Kerr
    Rod, ... Interesting... I had not really thought of using a USB memory stick as swap space, considering the conventional wisdom saying not to do this (both
    Message 1 of 2 , Jan 8, 2008
      Rod,

      On Tue, Jan 08, 2008 at 07:48:20PM +1030, Rod Whitby wrote:
      > > File : /Misc Files/SLUG performance report (web).pdf
      > > Uploaded by : kasclark <kasclark@...>
      > > Description : SLUG performance analysis
      >
      > I have added this report to the wiki at:
      >
      > http://www.nslu2-linux.org/wiki/Info/Performance (first link)

      Interesting... I had not really thought of using a USB memory stick
      as swap space, considering the conventional wisdom saying not to do
      this (both because the repeated writes will destroy the drive, and
      because it is slower than a hard disk).

      But I have a few smallish USB memory sticks I never use, so who cares
      if they get destroyed? (Plus a 1 Gbyte stick costs less than 10 euros,
      so even buying a new one is not a big deal.)

      A quick read test shows a cheap USB drive is about the same speed as
      the old IDE hard disks I have on the NSLU2 (sdc is the USB drive):

      /dev/sda (hard disk):
      Timing cached reads: 84 MB in 2.02 seconds = 41.66 MB/sec
      Timing buffered disk reads: 16 MB in 3.63 seconds = 4.40 MB/sec

      /dev/sdb (hard disk):
      Timing cached reads: 86 MB in 2.01 seconds = 42.77 MB/sec
      Timing buffered disk reads: 20 MB in 3.24 seconds = 6.17 MB/sec

      /dev/sdc (flash drive):
      Timing cached reads: 86 MB in 2.01 seconds = 42.75 MB/sec
      Timing buffered disk reads: 18 MB in 3.03 seconds = 5.94 MB/sec

      Simple write test (using the dd method on the performance page you
      linked to) shows throughput really sucks on the flash drive:

      sda (hard disk, ext3 file system):
      104857600 bytes (105 MB) copied, 14.3803 seconds, 7.3 MB/s
      104857600 bytes (105 MB) copied, 12.7808 seconds, 8.2 MB/s

      sdb (hard disk, ext3 file system):
      104857600 bytes (105 MB) copied, 12.5875 seconds, 8.3 MB/s
      104857600 bytes (105 MB) copied, 12.5849 seconds, 8.3 MB/s

      sdc (USB memory stick, ext2 file system):
      52428800 bytes (52 MB) copied, 23.7788 seconds, 2.2 MB/s
      52428800 bytes (52 MB) copied, 27.3963 seconds, 1.9 MB/s

      I went ahead and decided to test with Bonnie++ at this point, and this
      reveals that the random performance is about twice as fast as hard
      disks (makes sense, no seek time):

      $ /usr/sbin/bonnie++ -d $dir -s 56 -n 0 -f -m $disk

      Version 1.03 ------Sequential Output------ --Sequential Input- --Random-
      -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
      Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
      sda 56M 5666 34 2671 14 6469 19 121.6 6
      sdb 56M 7829 47 3070 13 6677 24 104.7 6
      sdc 56M 2018 8 1218 5 6046 25 278.7 19

      Sequential tests match up with the "dd" results.

      Looking at your results, it does not seem like the flash drive really
      helped much, but I think I'll go ahead and use one, mostly because
      memory sticks are silent! :)

      --
      Shane

      p.s. Too bad I'm such a coward when it comes to hardware, so I would
      fatten my slug... :(
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