Tag Archives: sysadmin

Fill an LVM volume group completely with a single logical volume

I learned a cool LVM trick today – how to resize a logical volume to use a certain percentage of a volume group. ┬áSince I just have one logical volume in the group, I did the following:

[root@nyu ~]# lvextend -l +100%FREE /dev/diclonius/vector
  Extending logical volume vector to 7.28 TiB
  Logical volume vector successfully resized

Thanks Redhat Documentation!

In other news, I ran a performance test on my 5-drive RAID-5 using HD204UI drives from Samsung:

[root@nyu tmp]# dd if=/dev/zero of=foo count=5 bs=$((1024*1024*1024))
5+0 records in
5+0 records out
5368709120 bytes (5.4 GB) copied, 18.1434 s, 296 MB/s
[root@nyu tmp]# dd if=foo of=/dev/null                         
10485760+0 records in
10485760+0 records out
5368709120 bytes (5.4 GB) copied, 15.2682 s, 352 MB/s

So, 350MB/sec reads and 296MB/sec writes! Not bad!!


How to set the RTC max_user_freq in newer kernels

I found out today how to set the real time clock max frequencies in Ubuntu since they removed the possibility to do it from sysutil.conf from newer kernels. Add the following to your /etc/rc.local or another startup script:

echo 2048 >/sys/class/rtc/rtc0/max_user_freq
echo 2048 >/proc/sys/dev/hpet/max-user-freq

Reboot, and you should get better performance from things like mplayer.