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I have some UDEV rules for a RAID array; 10 hard disks are assigned names from /dev/sda to /dev/sdj.

The disks can be absent at any time.

How do I write a UDEV rule to prevent a device such as an arbitrary USB from taking up one of the missing hard disk names?

For example, if my second hard disk /dev/sdb is unplugged for whatever reason, and then later someone plugs in a USB device in a completely different port, I need to usb to not become /dev/sdb.

I can think of a way to map each available USB port on the system to it's own name, but there must be a cleaner way? I am thinking of something like this, where I say "if it's a USB device, assign it a name from k to z:

KERNEL=="sd?", SUBSYSTEM=="block", DEVPATH="*usb", NAME="sd[k-z]", GOTO="END_20_PERSISTENT_DISK"

KERNEL=="sd?*", ENV{DEVTYPE}=="partition", SUBSYSTEM=="block", DEVPATH=="*usb*", NAME="sd[k-z]%n"

The system is intended to be fully autonomous, accepting any arbitrary USB or hard disk device - this is why I am using DEVPATHs versus labels and uuids.

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    Don't use device names like /dev/sda that are likely to be used by other devices. Change your rules to create /dev/myraida through /dev/myraidj or similar. – cjm May 22 '15 at 19:27
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Plug your usb drive and use

udevadm info -a -p /sys/block/sd* 

where * is your disk assigned number(sda1,sda3,sdb2,etc)

Then wrote a udev rule like this

KERNEL=="sd*", SUBSYSTEMS==" block", ATTRS{serial}=="**************", SYMLINK+="sdb%n"

Of course edit this based on udevadm info

Another good solution is to use DISK_UID or LABEL for mount,then /dev/sd* become not important,you will mount using LABEL or DISK_UUID I prefer LABEL,here's an example of my fstab

LABEL=memoria     swap             swap        defaults         0   0
LABEL=root        /                ext4        defaults,acl     1   1
LABEL=utenti      /home            ext4        defaults,acl     1   2

utenti and root are lvm volumes,and /dev/sd* is not important for use LABEL use e2label command on your partition

  • Unfortunately I can't use labels or uuids to identify devices - this system is intended for use as a portable, autonomous rig where clients can plug in arbitrary USB devices at any time for data offloads from the RAID array. I can't use labels as I would have to update the udev rules any time a client wants to use a new disk. – sg90 May 22 '15 at 15:23
  • Try first solution,use udevadm info and create a rule – elbarna May 22 '15 at 15:51
  • For the time being I'll write a udev rule for every USB port on my motherboard - the crux of this question was whether there is a better way to do this, ie. how to write udev rules to not get a particular name. If it was possible to do in a single rule vs a rule for each USB port device path. – sg90 May 22 '15 at 15:54
  • I'm not sure,but try to search google for udev regex negation – elbarna May 22 '15 at 16:15
  • I couldn't find any information for using regex on the name or symlink assignments, it appears regex is only available for the selectors ie. LABEL, DEVPATH etc. However I think I may have found a way to circumvent this whole issue - I will just name the hard disks used in the raid to things other than sda,sdb, ie. hd1,hd2 - this way any new USB device can take up these default names without disrupting the raid manager or any other scripts in use. – sg90 May 22 '15 at 17:27

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