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I have a system with two identical 1TB harddrives, where I image to a backup drive using the dd command. When I boot up, though, despite setting harddrive priority in the BIOS, the system sometimes boots the main drive, sometimes boots the backup. My system dual-boots Xubuntu and Windows XP, if that means anything to you.

Any ideas?

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Any connection between what boots, and what was booted last? – outsideblasts Jan 12 '10 at 2:59
No, there isn't. In Linux terms, I only ever want to be sda. So for example, I'll have sda booted, restart, then sdb will appear. So I shutdown and try again, which usually then works. – Zurahn Jan 14 '10 at 3:12
are you sure it's the BIOS getting the the drives confused? Xubuntu's uDev could be assigning sda and sdb differently each time. especially since you're using dd to backup -- this would copy the partitions' UUIDs as well, so Xubuntu (and likely WinXP) wouldn't have any way to tell the drives apart. – quack quixote Apr 5 '10 at 3:17

Quack Quixote is likely correct. I imagine your computer may be detecting them at just slightly different times leading to one being considered sda rather than what you expect (sdb). If this is the case, the fix is simple: don't use /dev/sdX references in your bootloader config or fstab. I prefer using the disk label, but some prefer using UUIDs.

Can you paste your bootloader config in a snippet here so we can determine more accurately if this is the problem?

Edit: I just saw how old this thread is; my apologies for the noise. Generally speaking though (for anyone who may encounter this issue in the future), the /dev/sdX references are the most likely problem.

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