CentOS - Jan 2014 - Installing on USB Flash Drive

Is it possible to install CentOS on a USB Flash Drive.  Have boot
sector, / and /boot on USB drive then put /home, etc on a software
raid array of the physical drives.

Thought there used to be motherboards with SDHC slots that you could
use to boot off.

On 1/25/14, Matt <matt.mailinglists at gmail.com>
wrote:
> Is it possible to install CentOS on a USB Flash Drive.  Have boot
> sector, / and /boot on USB drive then put /home, etc on a software
> raid array of the physical drives.
>
> Thought there used to be motherboards with SDHC slots that you could
> use to boot off.
I have a couple of machines that run entirely off USB drives with
mdraid so I'd say it's possible, barring any unusual hardware
compatibility issues.

However, note that there might be an issue with anaconda and big USB
storage. The boot partition anaconda creates will not boot past grub.
I needed to manually create the partition to start on sector 63 for
grub to see it. Happens on my 16GB sticks but not on small 1GB sticks.

I'm doing exactly this on a trial basis with production servers. So far, 
it's working great. Some tips:


1) Flash drives are less reliable than HDDs. Software RAID1 is the way 
to go.
      A) Use two different makes of USB drives so that you have 
different failure characteristics. If either fails, replace it 
immediately. You can set it up so that if a thumb drive fails, you can 
yank it and set up its replacement without downtime. Practice this and 
document how you did it.
     B) When you replace the failed USB drive and set it up, you can 
manually remove it from the raid array and test it without causing 
downtime to verify that grub, etc. are set up properly on a different 
(offline) machine. Do this.
     C) Write speed is important! USB drives have an incredibly diverse 
range of performance. Don't cripple yourself trying to save $5.


2) Flash drives typically have weak write endurance. Think of write 
capacity like a disposable salt shaker. Once it's run out of salt, it's 
game over and you can't recharge it.
     A) Find and root out any remaining regular write activity on the 
thumb drives and move affected partitions to something else.
     B) Mount all partitions on the flash drive RAID with noatime
     C) Move your /tmp, /var partitions to spinning disks or proper SSDs.
     D) Never put swap space on the thumb drives.
     E) Verify the lack of write activity with iostat.


Good luck.

On 01/24/2014 03:06 PM, Matt wrote:
> Is it possible to install CentOS on a USB Flash Drive.  Have boot
> sector, / and /boot on USB drive then put /home, etc on a software
> raid array of the physical drives.
>
> Thought there used to be motherboards with SDHC slots that you could
> use to boot off.
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