Monday, January 18

Measuring SSD performance : Follow up

After writing up this post I decided to go out and see what else I could do to speed things up.  I saw a suggestion for tweaking sreadahead, but ureadahead is what we use in Karmic and it already detects and optimizes for SSDs.

I did however see numerous suggestions for the addition of elevator=0 to the grub boot parameters will increase performance even more.

Here are my results:
$ sudo hdparm -t /dev/sda
 Timing buffered disk reads:  462 MB in  3.00 seconds = 153.85 MB/sec

$ sudo hdparm -t --direct /dev/sda
 Timing O_DIRECT disk reads:  642 MB in  3.00 seconds = 213.91 MB/sec

According to that, the improvement is minimal, but the dd test gives slightly different results:
$ sudo dd if=/dev/sda1 of=/dev/null bs=4k skip=0 count=51200
51200+0 records in
51200+0 records out
209715200 bytes (210 MB) copied, 1.04065 s, 202 MB/s

Wow, 178 to 202.  And it does feel even snappier in my environment. To implement this tweak, go to your /etc/default/grub and make the following change:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash elevator=0"

Then update the grub configuration:

sudo update-grub

Note, DO NOT make changes to /boot/grub/grub.cfg.  This file is overwritten every time update-grub is run, which happens whenever an update is made that the bootloader needs to know about(new kernel, etc).
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