If you want deterministic assignments, and things do not always start in the same order, you just need to setup rules.

http://www.reactivated.net/writing_udev_rules.html

and then you can use /dev/sda1, etc... in fstab.



----- Original Message -----
> From: "Konstantin Olchanski" <[log in to unmask]>
> To: "ToddAndMargo" <[log in to unmask]>
> Cc: "Scientific Linux Users" <[log in to unmask]>
> Sent: Monday, December 9, 2013 2:58:27 PM
> Subject: Re: Finally figured out what is causing bug 836696
> 
> On Mon, Dec 09, 2013 at 11:35:03AM -0800, ToddAndMargo wrote:
> > 
> > Bug 836696 has been driving me nuts for years.  This is
> > where you drop to fsck on boot for the backup drive,
> > but you can't do anything with the drive when you get
> > to maintenance mode.
> > 
> > And, I finally figured out what is causing this.  My
> > OS and my backup drive's devices are randomly reversing
> > themselves at boot.  For details, see comment #37:
> > 
> >     https://bugzilla.redhat.com/show_bug.cgi?id=836696#c37
> > 
> > Hope no one else has to figure this one out the hard way,
> > as I did.
> > 
> 
> Doh! This linux "feature" bites rookie and wizard all the same.
> 
> Linux assigns the sdN names in the order that devices are discovered
> and this order is not deterministic - SCSI, SATA and USB may all be
> scanned
> at the same time mixing up all the names each time. Mr. Torvalds
> cares
> about this not one bit, he has only a single drive inside his mac air
> and no usb ports to accidentally confuse things by leaving a usb
> drive
> connected during reboot.
> 
> Therefore, on linux, you cannot put "/dev/sda1" & co into /etc/fstab.
> You have to mount filesystems by UUID or by label. This was true and
> worked quite well for ages now. (Even with IDE disks, the /dev/hda,
> /dev/hdb, etc
> assignement was not super fixed - it depended on the order that IDE
> host adapters were initialized and this order has been known to
> change
> between different linux releases).
> 
> --
> Konstantin Olchanski
> Data Acquisition Systems: The Bytes Must Flow!
> Email: olchansk-at-triumf-dot-ca
> Snail mail: 4004 Wesbrook Mall, TRIUMF, Vancouver, B.C., V6T 2A3,
> Canada
>