Boot from USB


17 posts
by ErvKosch » Thu Mar 08, 2012 6:29 pm
I will preface this by saying: I know you can't boot directly from USB.  How ever has anyone made an ISO for the SD card to bring up a boot menu/boot loader and let you boot off a USB device?
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by RaTTuS » Thu Mar 08, 2012 6:35 pm
no one has one yet,

but you can boot from the sd card to chain to a USB device
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by Dochoss » Fri Mar 16, 2012 8:48 pm
Could you use a small SD card with GRUB loaded on it, and PXE boot via GRUB?  Over at the LinuxMCE wiki, there's a post that describes how to do this.  Could this work on a Pi?

http://wiki.linuxmce.org/index.....twork_boot

If so, XBMC diskless boot, here I come!  ...as soon as I can get a Pi, that is.
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by ErvKosch » Fri Mar 16, 2012 9:14 pm
You should be able to.  I just don't think anyone has rolled an ISO yet to do it.
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by Joe Schmoe » Fri Mar 16, 2012 10:19 pm
There is no such thing as "an ISO for the SD card".

You people really should research what an ISO file is.
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by SN » Fri Mar 16, 2012 10:31 pm
Lets not get all superior here. An ISO is a CD / DVD disk image which is a container for filesystem(s). Logically its the same for an SD card just officially we call it an image or IMG (and thats a pain because that name is also a graphics file format).
So call it what you like, we all know what you mean.
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by gsh » Sat Mar 17, 2012 7:14 am
Yes you can boot from the USB but only on the model A and then only with a modified USB cable (the red wire needs to be cut...)  See answers elsewhere
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by nick.mccloud » Sat Mar 17, 2012 10:01 am
Dochoss said:


Could you use a small SD card with GRUB loaded on it, and PXE boot via GRUB?  Over at the LinuxMCE wiki, there's a post that describes how to do this.  Could this work on a Pi?


No, there is no concept of GRUB on Pi. The GPU handles the start process and needs particular files on a FAT partition. You can alter those files so it looks else where afterwards.

gsh said:


Yes you can boot from the USB but only on the model A and then only with a modified USB cable (the red wire needs to be cut...)  See answers elsewhere


Please please please quote those answers else where - AFAIK the model A is less capable (as in no ethernet, only 1 USB) - due to less components - there are no other differences. Unless you are being ironic. If so, please add a smiley, we don't want users hacking up their USB cables just to try it.
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by Joe Schmoe » Sat Mar 17, 2012 10:14 am
@nmcc:

1) It is my understanding that there could, at some level, be something resembling GRUB (at the same level of imprecision, as, say, referring to an SD card image file as "an ISO file" - heh heh), but that PXE is strictly x86 only.  The idea is that someone, somewhere, will develop an SD card setup that contains the base files needed to boot,  which will boot up to some kind of menu, that allows you to then transfer control to a selected partition/OS.  Like Grub does on x86 systems...

2) I think the poster is referring to the idea raised in the "Crucial Model A hardware fix urgenly needed - do it now!" thread.  The idea is that if the 5th wire isn't asserted, then the USB device could be a slave.  Or something like that...  In any case, read that thread for the details on why (according to the OP of that thread) it can only be done on the Model A.

Disclaimer: I don't write or endorse any of this stuff.  I just have a good memory...
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by Hiro » Sat Mar 17, 2012 11:27 am
Assuming an image could be made on the SD card to access the boot files on an external hard drive is there any advantage to doing this?

Would there be a speed advantage? I suppose i need to look up access/read times of SD cards and usb hard drives  and compare the two.

Is there anything else i'm missing ie. why would anyone want/need to boot from an external drive other than speed advantage?
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by lewmur » Sat Mar 17, 2012 11:38 am
nmcc said:


Dochoss said:


Could you use a small SD card with GRUB loaded on it, and PXE boot via GRUB?  Over at the LinuxMCE wiki, there's a post that describes how to do this.  Could this work on a Pi?


No, there is no concept of GRUB on Pi. The GPU handles the start process and needs particular files on a FAT partition. You can alter those files so it looks else where afterwards.

gsh said:


Yes you can boot from the USB but only on the model A and then only with a modified USB cable (the red wire needs to be cut...)  See answers elsewhere


Please please please quote those answers else where - AFAIK the model A is less capable (as in no ethernet, only 1 USB) - due to less components - there are no other differences. Unless you are being ironic. If so, please add a smiley, we don't want users hacking up their USB cables just to try it.



Yes, Grub is an x86 bootloader.  But what about moboot?  That is a bootloader for ARM devices.  Checkout the XDA forums for moboot.
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by bob_binz » Sat Mar 17, 2012 12:02 pm
Joe Schmoe said:


2) I think the poster is referring to the idea raised in the "Crucial Model A hardware fix urgenly needed - do it now!" thread.  The idea is that if the 5th wire isn't asserted, then the USB device could be a slave.  Or something like that...  In any case, read that thread for the details on why (according to the OP of that thread) it can only be done on the Model A.


I think the title's changed, but I guess this is the post:

http://www.raspberrypi.org/for.....-read-this

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by Smartybones » Sat Mar 17, 2012 2:30 pm
SN said:


Lets not get all superior here. An ISO is a CD / DVD disk image which is a container for filesystem(s). Logically its the same for an SD card just officially we call it an image or IMG (and thats a pain because that name is also a graphics file format).
So call it what you like, we all know what you mean.



hats off to you sir, we can do without pedantic comments. next thing it will be corrections on grammar and punctuation.

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by Joe Schmoe » Sat Mar 17, 2012 2:34 pm
Well, whatever.

To me, it is incredibly sloppy use of language.  But to each his own.
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by Smartybones » Sat Mar 17, 2012 2:47 pm
Hiro said:


Is there anything else i'm missing ie. why would anyone want/need to boot from an external drive other than speed advantage?



there are  good reasons for wanting to boot from an external hard drive, imagine on your SD card your Pi needs to boot from, you have a menu system that reads the contect of a hard drive partition to list the various different operating systems for your Pi for you to select which one you want to load.

yes, you can do the same thing by just swapping SD cards, but then you have to set aside a whole bunch of SD cards... Also, as a semi pro photographer, i use a lot of SD cards, I have two laptops that the SD card slots need replacing due to over use. These days I use a usb card reader as its easier to replace.

booting from a network drive is also something that is also needed, and will be one of my later projects if it hasnt already been done by the time i get around to it.
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by Lynbarn » Sat Mar 17, 2012 3:02 pm
Joe Schmoe said:


Well, whatever.

To me, it is incredibly sloppy use of language.  But to each his own.


Actually, I think it is more the over-use or inappropriate use of technical jargon that is the key here – not everyone knows what "ISO" means in this context, for example. We should all remember that everyone on this forum has a different level of expertise in a wide range of different subjects, and we need to cater for all.
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by Hiro » Sat Mar 17, 2012 4:06 pm
@Smartybones

I never thought of multi-booting but i can certainly see the advantage in that.

Just had a quick google for relative speeds of SD card and USB speed and external hard drive speed and i think there may be an advantage there too if i have my figures right. The cards i intend to use are class 4 with a transfer rate of 4 Mb/s and USB is supposedly unable to sustain above about 40 Mb/s. Hard drives are able to deliver much faster than USB can handle so their speed is irrelevant.

Theoretically that means that it would boot 10 times faster but of course the machine still needs to boot to the card first to access the boot files on the external and as the image isn't going to be that large (i assume) then the advantage may be minimal at best.

Does that sound right(ish) to anyone or am i miles off?
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