Hitchhiker's Guide to Openbsd

14.17.2 - Flash memory as bootable storage
One can also use flash memory in various forms as bootable disk with OpenBSD. This can be done with both 
USB devices (assuming your computer can boot from a USB flash device, not all can), or with a non-USB (i.e., 
CF) device with an IDE or SATA adapter. (Non-USB devices attached with a USB adapter are treated as USB 
devices). In some cases, you may actually use a device in both ways (load the media in a USB adapter, but run it 
in an IDE adapter) 
A flash device attached to a USB port will show up as a 
sd(4)
SCSI-like device. When attached to an IDE adapter, 
it will show up as a 
wd(4)
 device. 
In the case of flash media in an IDE adapter, it can be booted from any system that could boot from an IDE hard 
disk. In every sense, the system sees the flash media as an IDE disk. Simply configure the hardware appropriately, 
then install OpenBSD to the flash disk as normal. 
In the case of booting from a USB device, your system must be able to boot from the USB device without being 
distracted by other devices on the system. Note that if your intention is to make a portable boot environment on a 
USB device, the USB device will show up as a SCSI disk, sometimes sd0. However, if you plug this device into a 
system which already has a few SCSI-like disks (i.e., devices attached to an ahci(4) interface) on it, it will 
probably end up with a different identifier, which will complicate carrying the flash device from system to 
system, as you will have to update 
/etc/fstab
. 
http://www.openbsd.org/faq/faq14.html (30 of 34)9/4/2011 10:02:25 AM

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14 - Disk Setup
Some notes: 
●
Speed: In general, flash devices are much slower than hard disks, especially when it comes to writing. 
Using 
soft updates
 will help this considerably, as will using the "noatime" mount option. 
●