Create a single, aligned partition on a drive larger than 2TB.

% sudo parted /dev/sdx
(parted)% mklabel gpt
(parted)% mkpart primary 1 -1


Just replaced my heavily used Ubuntu HTPC with a 6 watt AppleTV 2. Both run XBMC.

Specs of the old, silent HTPC:

  • Intel Core 2 Duo E4300 1.8GHz w/2MB Cache
  • Intel DQ965GF motherboard with passive chipset heatsinks
  • Scythe Ninja passive CPU heatsink
  • 4GB (2x 2GB DIMMS) ADATA DDRII 800 MHz memory
  • 512 MB MSI N210-MD512H GeForce 210 PCIe 2.0 passive video card
  • 40 GB Kingston SSDNOW V-series (Intel rebranded) SATA SSD
  • 18x DL DVD+-RW Optiarc Ad-7170S 2MB Cache SATA optical drive
  • Antec Sonata case
  • Dual 120mm Yate Loon case fans
  • Seasonic 330W power supply
  • Ubuntu 10.04 AMD64 with XBMC

Video is just as smooth on the AppleTV as on the HTPC.

15,471,232 Pixels

Screens I look at on a normal weekday:

  • iPhone 4 (3.5″) (960 x 640)
  • iPad (9.7″) (1024 x 768)
  • Netbook (10.1″) (1024 x 600)
  • Work MacBook (15.4″) (1440 x 900)
  • Work Desktop (27″ + 24″) (2560 x 1440 + 1920 x 1200)
  • Home Desktop (30″) (2560 x 1600)
  • HTPC (42″) (1920 x 1080)

Linux Software RAID10 Benchmarks

Tests are done across four 7200RPM SATAII drives on a PCI-X card sitting on a PCI (32-bit, 133MB/sec theoretical max) bus, probably the slowest bus configuration possible, and then again after being moved to a motherboard with dual PCI-X slots. Server is running Ubuntu 9.10 AMD64 Server.

Benchmark is a simple ‘dd’ sequential read and write.

write: dd if=/dev/zero of=/dev/md2 bs=1M
read: dd if=/dev/md2 of=/dev/null bs=1M

mdadm –create /dev/md2 –verbose –level=10 –layout=n2 –raid-devices=4 /dev/sd[ftlm]1

write: 13.2 MB/s 144 MB/s
read: 4.0 MB/s 89.3 MB/s

mdadm –create /dev/md2 –verbose –level=10 –layout=f2 –raid-devices=4 /dev/sd[ftlm]1

write: 48.3 MB/s 131 MB/s
read: 92.7 MB/s 138 MB/s

mdadm –create /dev/md2 –verbose –level=10 –layout=o2 –raid-devices=4 /dev/sd[ftlm]1

write: 47.4 MB/s 135 MB/s
read: 98.7 MB/s 142 MB/s

And more comparisons:


write: 38.9 MB/s
read: 64.8 MB/s

Single Disk (PCI)

write: 59.4 MB/s
read: 71.9 MB/s

Replace an LVM Drive with a Larger One

LVM allows you to hot add devices to expand volume space. It also allows you to hot remove devices, as long as there are enough free extents in the volume group (vgdisplay) to move data around. Here I’m going to replace a 400 GB drive (sdg) with a 750 GB one (sdh) from logical volume “backup” on volume group “disks”. It does not matter how many hard drives are in the volume group, and the filesystem can stay mounted.

  1. Partition and create a physical volume on the device
    $ sudo pvcreate /dev/sdh1
  2. Add the new drive to the volume group
    $ sudo vgextend disks /dev/sdh1
  3. Move all extents from the old drive to the new one (this step may take hours)
    $ sudo pvmove -v /dev/sdg1
  4. Remove the old drive
    $ sudo vgreduce disks /dev/sdg1
  5. Expand the logical volume to use the rest of the disk. In this case, another 350GB.
    $ sudo lvextend -l+83463 /dev/disks/backup
  6. Expand the file system
    $ sudo resize2fs /dev/disks/backup
    $ sudo xfs_growfs /dev/disks/backup

mdadm Cheatsheet

Scan a system for RAID arrays and save findings so the array reappears across reboots:

# mdadm --detail --scan && /etc/mdadm/mdadm.conf

Create a RAID5 array out of sdm1, sdj1, and a missing disk (all partitioned with raid-autodetect partitions)

# mdadm --create /dev/md1 --level=5 --raid-devices=3 /dev/sd[mj]1 missing

Create a RAID1 array

# mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sd[ts]1

Remove a RAID array

# mdadm --stop /dev/md1
# mdadm --zero-superblock /dev/sd[ts]1

Replace a failed drive that has been removed from the system

# mdadm /dev/md3  --add /dev/sdc1 --remove detached

Add a new drive to an array, and remove an existing drive at the same time

# mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1

Add a drive to a RAID 5 array, growing the array size

# mdadm --add /dev/md1 /dev/sdm1
# mdadm --grow /dev/md1 --raid-devices=4

Fixing an incorrect /dev/md number (ie /dev/md127)

1. Remove any extra parameters for the array except for UUID in /etc/mdadm/mdadm.conf. Ex.

#ARRAY /dev/md1 level=raid1 num-devices=2 metadata=1.2 UUID=839813e7:050e5af1:e20dc941:1860a6ae
ARRAY /dev/md1 UUID=839813e7:050e5af1:e20dc941:1860a6ae

2. Then rebuild the initramfs

sudo update-initramfs -u

Start Folding@Home on Boot with Screen on Ubuntu Linux

Quick instructions to get Folding@home (or any other program) to run at boot before user login on Ubuntu Linux. This probably works on other distros with an rc.local file too.

1. Install F@H client, mine is in /opt/folding

2. Create a simple script, I called mine and is only has:

cd /opt/folding
./fah6 -smp

3. Put the screen command in /etc/rc.local. This will execute as user nick (su nick -c), “-dmS” will create the session detached and name it folding, and “bash –rcfile” will allow the screen session to keep running even if folding quits.

su nick -c "screen -dmS folding bash --rcfile /home/nick/bin/"

Folding@home now starts whenever the computer boots, before anyone logs in. Nick can reattach to it and  control it or watch the progress by running “screen -r folding”.