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I have two drives, a 120GB SSD and a 2TB HD. I set the BIOS to boot from the SSD, and an the Drives window of Ubuntu it tells me the SSD is SDB and the HD is SDA. I would expect the SSD to be SDA because it is being boote

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The order of the devices /dev/sda, sdb, ... is independent from the boot order. The important criterion is, which SATA port is used for which drive. I cannot give the criterion (which has higher priority) if you have multiple SATA controllers, hence I only comment your question. –  mpy Mar 23 '13 at 13:16
    
Thanks for the comment. So if I re-order the SATA cables the order should change. Does this mean that if I manage to set my SSD to SDA then I won't have to boot using UEFI but will still be able to access my HD for data? –  Max Mar 23 '13 at 13:29
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This is starting to sound like an XY problem. What exactly are you trying to do? –  terdon Mar 23 '13 at 13:32
    
You are right. I am trying to avoid UEFI to make dual-boot for win7 and ubuntu easier: superuser.com/questions/570312/… . For the moment, I think this is enough to be getting on with. Thanks :) I would mark you as the solution but ... –  Max Mar 23 '13 at 14:20

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Boot order doesn't define devices names and the names can change if you add or remove disks.

If you change the disks frequently (add or remove fixed disks or use external disks), it is better to mount the disks using their UUID instead of device names in /etc/fstab (use UUID=xxxxxxx instead of /dev/sdx). UUIDs are fixed for each disk or partition.

You can find the UUIDs of your disks using blkid or ls -l /dev/disk/by-uuid

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