Below is a script which makes a few very small (<128K) loopback
devices, then tries to assemble them with mdadm. It demonstrates
the underflow bug for which I previously sent the patch. It's a
bash script, not a posix-shell script, as indicated in the shebang.
It creates and destroys devices with hard-coded paths
(/dev/loop[1-3], /dev/md99, etc.), so only run it with caution!
==== Here is the output when I run it:
% sudo ./mdadm-patch-test.bash
RAID-5, metadata 1.2, unpatched:
/sbin/mdadm --create --verbose /dev/md99 --chunk=256 --level=5 --layout=left-symmetric --raid-devices=3 /dev/loop1 /dev/loop2 /dev/loop3 --metadata=1.2
mdadm: size set to 9223372036854774784K
mdadm: automatically enabling write-intent bitmap on large array
./mdadm-patch-test.bash: line 24: 554310 Floating point exception${cmd}
RAID-5, metadata 1.2, patched:
./mdadm --create --verbose /dev/md99 --chunk=256 --level=5 --layout=left-symmetric --raid-devices=3 /dev/loop1 /dev/loop2 /dev/loop3 --metadata=1.2
device /dev/loop1 is too small (64K) for required metadata!
mdadm: /dev/loop1 is not suitable for this array.
device /dev/loop2 is too small (64K) for required metadata!
mdadm: /dev/loop2 is not suitable for this array.
device /dev/loop3 is too small (64K) for required metadata!
mdadm: /dev/loop3 is not suitable for this array.
mdadm: create aborted
RAID-5, metadata 1.1, unpatched:
/sbin/mdadm --create --verbose /dev/md99 --chunk=256 --level=5 --layout=left-symmetric --raid-devices=3 /dev/loop1 /dev/loop2 /dev/loop3 --metadata=1.1
mdadm: size set to 9223372036854774784K
mdadm: automatically enabling write-intent bitmap on large array
./mdadm-patch-test.bash: line 24: 554321 Floating point exception${cmd}
RAID-5, metadata 1.1, patched:
./mdadm --create --verbose /dev/md99 --chunk=256 --level=5 --layout=left-symmetric --raid-devices=3 /dev/loop1 /dev/loop2 /dev/loop3 --metadata=1.1
device /dev/loop1 is too small (64K) for required metadata!
mdadm: /dev/loop1 is not suitable for this array.
device /dev/loop2 is too small (64K) for required metadata!
mdadm: /dev/loop2 is not suitable for this array.
device /dev/loop3 is too small (64K) for required metadata!
mdadm: /dev/loop3 is not suitable for this array.
mdadm: create aborted
RAID-1, metadata 1.2, unpatched:
/sbin/mdadm --create --verbose /dev/md99 --level=1 --raid-devices=2 /dev/loop1 /dev/loop2 --metadata=1.2
mdadm: size set to 9223372036854774784K
mdadm: automatically enabling write-intent bitmap on large array
./mdadm-patch-test.bash: line 24: 554339 Floating point exception${cmd}
RAID-1, metadata 1.2, patched:
./mdadm --create --verbose /dev/md99 --level=1 --raid-devices=2 /dev/loop1 /dev/loop2 --metadata=1.2
device /dev/loop1 is too small (32K) for required metadata!
mdadm: /dev/loop1 is not suitable for this array.
device /dev/loop2 is too small (32K) for required metadata!
mdadm: /dev/loop2 is not suitable for this array.
mdadm: create aborted
RAID-1, metadata 1.1, unpatched:
/sbin/mdadm --create --verbose /dev/md99 --level=1 --raid-devices=2 /dev/loop1 /dev/loop2 --metadata=1.1
mdadm: size set to 9223372036854774784K
mdadm: automatically enabling write-intent bitmap on large array
./mdadm-patch-test.bash: line 24: 554349 Floating point exception${cmd}
RAID-1, metadata 1.1, patched:
./mdadm --create --verbose /dev/md99 --level=1 --raid-devices=2 /dev/loop1 /dev/loop2 --metadata=1.1
device /dev/loop1 is too small (32K) for required metadata!
mdadm: /dev/loop1 is not suitable for this array.
device /dev/loop2 is too small (32K) for required metadata!
mdadm: /dev/loop2 is not suitable for this array.
mdadm: create aborted
%
==== Here's the script:
#!/bin/bash
#sudo="sudo" # empty-string if run as root
sudo=""
md_dev="/dev/md99"
# Create test devices:
mk_devs() {
n_dev="${1}"
devsize="${2}"
for (( n=1; n<="${n_dev}"; ++n )) do
dev="/dev/loop${n}"
file="/tmp/component-0${n}"
truncate -s "${devsize}" "${file}"
${sudo} losetup "${dev}" "${file}"
done
}
# Do one test run:
do_run() {
lbl="${1}"
mdvers="${2}"
echo -e "\n${lbl}, metadata ${mdvers}, unpatched:"
cmd="${sudo} /sbin/mdadm ${args} --metadata=${mdvers}"
echo "${cmd}"
${cmd}
${sudo} /sbin/mdadm --stop "${md_dev}" 2>/dev/null
echo -e "\n${lbl}, metadata ${mdvers}, patched:"
cmd="${sudo} ./mdadm ${args} --metadata=${mdvers}"
echo "${cmd}"
${cmd}
${sudo} /sbin/mdadm --stop "${md_dev}" 2>/dev/null # not necessary, create fails
}
# --- RAID level 5:
mk_devs 3 65536
args="--create --verbose ${md_dev} --chunk=256 --level=5 --layout=left-symmetric --raid-devices=3 /dev/loop1 /dev/loop2 /dev/loop3"
do_run RAID-5 1.2
do_run RAID-5 1.1
${sudo} losetup -d /dev/loop1 /dev/loop2 /dev/loop3
rm -f /tmp/component-01 /tmp/component-02 /tmp/component-03
# --- RAID level 1:
mk_devs 2 32768
args="--create --verbose ${md_dev} --level=1 --raid-devices=2 /dev/loop1 /dev/loop2"
do_run RAID-1 1.2
do_run RAID-1 1.1
${sudo} losetup -d /dev/loop1 /dev/loop2
rm -f /tmp/component-01 /tmp/component-02
