smarter md minor search than "find_free_devnum" needed

[Sebastian Riemer <sebastian.riemer@profitbricks.com>]

Hi list,

I'm thinking about creation of many MD RAID 1 devices by automatic
scripts. The MD minor numbers should be auto-determined. But if I do
this with mdadm 3.2.5 and kernel 3.4.2 without udev, then it gets slower
the more devices I create. I also had to patch mdadm to make
"--symlinks=no" really work (preventing "/dev/md/*" symlinks to be created).

Looks like this:
# MDADM_NO_UDEV=1 mdadm -C auto --symlinks=no --assume-clean --force -l
1 -n 2 /dev/loop$i /dev/loop$j

Btw.: With udev it hangs for some seconds.

With this it is fast but can't use it for production (I only have the
UUIDs):
# MDADM_NO_UDEV=1 mdadm -C /dev/md$k --assume-clean --force -l 1 -n 2
/dev/loop$i /dev/loop$j

What about caching the next free minor number in kernel space, taking
it, finding the next free and updating it?
Or is there another possibility (putting this into a custom daemon
should be avoided)?

If I identify the MD devices by UUID, I don't want to care which minor
number they actually have upon creation/assembly.

Cheers,
Sebastian

-- 
Sebastian Riemer
Linux Kernel Developer

ProfitBricks GmbH • Greifswalder Str. 207 • 10405 Berlin, Germany
www.profitbricks.com • sebastian.riemer@profitbricks.com

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