Dear Linux-RAID Developers,
I always wanted to have a small home server with a RAID-array to store
pesonal and work files.
So I decided to create a fileserver with a raspberry pi and a RAID-1
Array. For this I bought two USB 1TB HDs.
After a while I noticed that Mdadm was marking my drives as failed or
even worse as faulty. This was strange since both HDs are new.
So I tested them. I deleted the RAID partitions completely with WIPEFS.
Then I created Ext4 partitions and run a benchmark of the partitions in
ubuntu. Everything is fine.
I created then again my RAID array. To my surprise one drive was again
faulty. I googled a little and I found that my USB drives went to sleep
mode and when they were woken up, one of them changed name /dev/sdb/ ->
/dev/sdc. Mdadm was unable to find the "new" drive and marked it as
faulty. Re-add didn't work. Adding it again went into an unnecessary and
long sync of 1TB.
I googled the problem and learnt about UDEV. It turns out that Linux
gracefully creates symlinks to the disks-partitions under
/dev/disks/by-id/... I thought that I could use this symlinks to fix the
problem with Mdadm, but mdadm just followed the links to find again the
changing /dev/sd* names.
I continued my journey and found more about the UDEV rules. I created a
couple of them, using the serial number of the disks. I turns out that
changing the name is not anymore allowed. (NAME="sdb" is ignored) There
is even a warning about this. See here:
http://unix.stackexchange.com/questions/119593/is-there-a-way-to-change-device-names-in-dev-directory
"NAME="pendrak" ignored, kernel device nodes can not be renamed; please
fix it in /etc/udev/rules.d/99-local.rules:1"
My last desperate idea was to create a cron job that reads directly from
the disks, to keep them awake and avoid a name change. Something like
this:
dd if=/dev/disk/by-id/usb-TOSHIBA_External_USB_3.0_20151214504D3-0:0
bs=1024 count=$(($[1<<10]*10)) skip=$(($SKIP)) ibs=1024 of=/dev/null
iflag=direct status=none 2>&1
But even with that workaround the name of a disk just changed and Mdadm
marked it as faulty. --- I'm out of ideas.
So I'm stuck with this wonderful situation:
- MDADM will follow symlinks and ignore the /dev/disk/by-id/...
identification.
- UDEV does not allow to change the name of a device.
- The names will apparently change no matter what I do.
I'm starting to regret my decision to create this array. I expected some
challenges but it is turning to be ridiculously difficult. Almost
unusable.
Maybe you have a solution for this.
In any case it would be great if you consider some long-term
out-of-the-box solution for this new reality of USB HDs. My ideas would
be:
-- Allow to create arrays with symlinks
("/dev/disk/by-id/usb-TOSHIBA_External_USB_3.0_20151214504D3-0:0")
-- Include a keep-alive functionality that avoids names to change
randomly.
-- Store HD ids to recognize disks.
Thank you.
Best regards,
Juan Carlos Carvajal Bermúdez
+43 650 477 0005
juca@xxxxxxxxxxxxxxxx
Beingasse 17/2/3
AT 1150, Wien
www.juan-carlos.info
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