[CentOS] usb drives & Orico ORICO 9548U3-BK

[Pete Biggs]

> 
> 
> I decided to build an archive server for the purpose of backing up
> other fedora/centos desktops at the office.  I built a machine and have
> installed Centos 7.3 on it with all updates current.  I also purchased
> a 3.0 usb sata drive cabinet (Orico ORICO 9548U3-BK) and installed two
> 5T black WD drives.   There was no problem installing the usb cabinet
> or the drives.  I formatted each drive with xfs as /dev/sdc and
> /dev/sdd, and then combined them into a software mirrored raid with
> mdadm as /dev/md0.

I've always thought that the perceived wisdom is to not try and do
software raid across USB - especially when both drives are at the other
end of the same USB cable. Sure USB 3 is faster and there's a better
chance it will appear to work at a reasonable speed, but it's not
something I would contemplate.

> 
> Everything was working perfectly until I removed the terminal, keyboard
> and mouse and tried to reboot the machine.  It took a while to figure
> out, but when the mouse and keyboard were removed the boot process
> assigns the usb drives differently which makes /dev/md0 created by
> mdadm fail.

Which means that the drive letters are explicitly mentioned in
/etc/mdadm.conf - you can change it to be wildcarded or leave mdadm to
figure it all out itself.  See 'man mdadm.conf'.

> 
> My fstab file looks like :
> 
> /dev/mapper/centos_poar-root              /        xfs    defaults  0 0
> UUID=f915a354-28bf-4110-bec9-3767ef1fe52c /boot    xfs    defaults  0 0
> /dev/mapper/centos_poar-home              /home    xfs     defaults 0 0
> /dev/mapper/centos_poar-u                 /u       xfs     defaults 0 0
> /dev/mapper/centos_poar-swap              swap     swap    defaults 0 0
> /dev/sda                                  /u0      btrfs   defaults 0 0
> # entries below were combined into one mirrored raid system
> #/dev/sdc                                /u1      xfs     defaults 0 0
> #/dev/sdd                                /u2      xfs     defaults 0 0
> /dev/md0                                 /u1      xfs     defaults 0 0

Another likely issue is that you explicitly mention /dev/sda in the
fstab - if the drives are re-ordered, then /dev/sda will not be what
you think it is.  It's a much better idea to use UUIDs when mounting
drives. You can find the UUID with 

  lsblk --fs /dev/sda

BTW, are you really using partitionless disks - is it really /dev/sda
and not /dev/sda1 ?

> 
> 
> This works perfectly when a usb mouse and a usb keyboard are attached,
> but when I remove the mouse and keyboard the system will not boot
> because the usb drives are relabeled as /dev/sda and /dev/sdb.

I would have thought that any SATA drives would have been processed
before the USB drives - certainly it looks that way on my system. Try
going through the output of dmesg to see if you can see what is really
happening when in the boot sequence.

> 
> 
> My thought is that if I could force the usb drives to be labeled as
> /dev/sdc and /dev/sdd whether the mouse and keyboard are attached or
> not, I might be able to fix the problem

It's much easier to make sure you don't explicitly use drive letters -
because, as you've found out, they can change.  Use filesystem labels
or UUIDs or disk IDs. The disk IDs can be found in /dev/disk/by-id and
they should remain the same.

P.