[Discuss] How do you backup "/" with rsync?

[Alan W. Irwin]

On 2007-12-11 10:06-0800 Steven Kurylo wrote:

>> Yes, you are quite right, if your internal HD fails your BIOS will
>> probably hang and you will need to go into BIOS setup to delete the bad
>> drive from the list. You can switch the BIOS boot sequence at that time.
>
> I don't know of any modern BIOS which will hang.  It won't be able to
> detect the drive and will move on to the next boot device.  Long time
> ago I've seen hard drives go wrong and the bios hang as it gets
> strange repsonses.
>
>>  From an academic point of view I am not sure where Linux gets its sda,
>> sdb, etc information from.  I suspect it may be from the BIOS, "Primary
>> Master == sda", "Primary Slave == sdb", etc, in which case even if
>> "Primary Master" is dead, skipped or entirely absent, it will still
>> identify "Primary Slave" as sdb i.e. it will not rename it sda???
>
> Linux labels its drives in the order it finds them, regardless of what
> you've done in the bios.  The first drive it finds will be sda;
> usually that will be the PM, if there is only a PS that will become
> sda.  But once you have several HD controllers, linux could see
> something else first.  It depends on the order you load modules.

I have read recently that primary master and slave are concepts that are
only relevant to PATA drives.  So for the pure SATA case (which applies for
me) the default order of drive assignments seems even more problematic.

>
> But if you use udev, you can make drive letters persistent.  You could
> make your WD 200GB drive always show up as sda, regardless of how you
> plug it it (sata, esata, usb, firewire, etc).

This sounds like an excellent method for making drive letters persistent.

Steven, to save me a lot of reading time would you happen to know the udev
cookbook for persistent drive letters for the case of identical internal and
external SATA drives?  I am running Debian testing which uses udev.

Here are some results concerning disk identity for my system:

irwin at raven> ls -l /dev/disk/by-id/
total 0
lrwxrwxrwx 1 root root  9 2007-12-09 21:21 ata-ST3500630AS-9QG3XJPX ->
../../sdb
lrwxrwxrwx 1 root root 10 2007-12-09 21:21 ata-ST3500630AS-9QG3XJPX-part1 ->
../../sdb1
lrwxrwxrwx 1 root root 10 2007-12-09 21:21 ata-ST3500630AS-9QG3XJPX-part2 ->
../../sdb2
lrwxrwxrwx 1 root root 10 2007-12-09 21:21 ata-ST3500630AS-9QG3XJPX-part5 ->
../../sdb5
lrwxrwxrwx 1 root root  9 2007-12-09 21:21 scsi-S_9QG3XJPX -> ../../sdb
lrwxrwxrwx 1 root root 10 2007-12-09 21:21 scsi-S_9QG3XJPX-part1 -> ../../sdb1
lrwxrwxrwx 1 root root 10 2007-12-09 21:21 scsi-S_9QG3XJPX-part2 -> ../../sdb2
lrwxrwxrwx 1 root root 10 2007-12-09 21:21 scsi-S_9QG3XJPX-part5 -> ../../sdb5

I booted with this external drive turned on, then subsequently turned it
off, but I don't think that turn-off has affected the above list since all
the external disk partitions seem to be there.

A google search indicates ST3500630AS corresponds to the Seagate Barracuda
7200.10 500GB SATA hard drive (which is the model number of both my internal
and external hard drives according to my invoices).  A google search for
9QG3XJPX gave no hits so this may be the serial number and thus a unique
identifier to help distinguish between my two drives. However, I don't know
for sure since the internal disk (/dev/sda) does not appear in the above
list for some unknown reason.

Is there a better source of internal information I can use to get the model
and serial numbers of the two drives? If serial numbers are unavailable or
cannot be used by udev to distinguish disks, then udev might be able to use
the different controllers (ich9 SATA controller versus jmicron eSATA
controller) to distinguish the two disks.

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state implementation
for stellar interiors (freeeos.sf.net); PLplot scientific plotting software
package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of
Linux Links project (loll.sf.net); and the Linux Brochure Project
(lbproject.sf.net).
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Linux-powered Science
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