So I thought about a cool way to backup my files without using anything too fancy and I started to think about ZFS. Don’t know why I didn’t before because it’s ultra ultra resilient. Cheers Oracle. This is in Debian 7 Wheezy.

Step 1 Install zfs

# apt-get install lsb-release
# wget http://archive.zfsonlinux.org/debian/pool/main/z/zfsonlinux/zfsonlinux_6_all.deb
# dpkg -i zfsonlinux_6_all.deb

# apt-get update
# apt-get install debian-zfs

Step 2 Create Mirrored Disk Config with Zpool.
Here i’m using 4 x 75GB SATA Cloud Block Storage Devices to have 4 copies of the same data with ZFS great error checking abilities

zpool create -f noraidpool mirror xvdb xvdd xvde xvdf

Step 3. Write a little disk write utility

#!/bin/bash


while :
do

        echo "Testing." $x >> file.txt
        sleep 0.02
  x=$(( $x + 1 ))
done

Step 4 (Optional). Start killing the Disks with fire, kill iscsi connection etc, and see if file.txt is still tailing.

./write.sh & ; tail -f /noraidpool/file.txt

Step 5. Observe that as long as one of the 4 disks has it’s virtual block device connection your data is staying up. So it will be OK even if there is 3 or less I/O errors simultaneously. Not baaaad.

root@zfs-noraid-testing:/noraidpool# /sbin/modprobe zfs
root@zfs-noraid-testing:/noraidpool# lsmod | grep zfs
zfs                  2375910  1
zunicode              324424  1 zfs
zavl                   13071  1 zfs
zcommon                35908  1 zfs
znvpair                46464  2 zcommon,zfs
spl                    62153  3 znvpair,zcommon,zfs
root@zfs-noraid-testing:/noraidpool# zpool status
  pool: noraidpool
 state: ONLINE
  scan: none requested
config:

        NAME        STATE     READ WRITE CKSUM
        noraidpool  ONLINE       0     0     0
          mirror-0  ONLINE       0     0     0
            xvdb    ONLINE       0     0     0
            xvdd    ONLINE       0     0     0
            xvde    ONLINE       0     0     0
            xvdf    ONLINE       0     0     0

errors: No known data errors

Step 6. Some more benchmark tests

time sh -c "dd if=/dev/zero of=ddfile bs=8k count=250000 && sync"

Step 7. Some concurrent fork tests

#!/bin/bash

while :
do

time sh -c "dd if=/dev/zero of=ddfile bs=8k count=250000 && sync" &
        echo "Testing." $x >> file.txt
        sleep 2
  x=$(( $x + 1 ))
 zpool iostat
clear
done

or better

#!/bin/bash

time sh -c "dd if=/dev/zero of=ddfile bs=128k count=250000 && sync" &
time sh -c "dd if=/dev/zero of=ddfile bs=24k count=250000 && sync" &
time sh -c "dd if=/dev/zero of=ddfile bs=16k count=250000 && sync" &
while :
do

        echo "Testing." $x >> file.txt
        sleep 2
  x=$(( $x + 1 ))
 zpool iostat
clear
done

bwm-ng ‘elegant’ style output of disk I/O using zpool status

#!/bin/bash

time sh -c "dd if=/dev/zero of=ddfile bs=8k count=250000 && sync" &
while :
do
clear
 zpool iostat
sleep 2
clear
done

To test the resiliency of ZFS I removed 3 of the disks, completely unlatching them

        NAME                      STATE     READ WRITE CKSUM
        noraidpool                DEGRADED     0     0     0
          mirror-0                DEGRADED     0     0     0
            1329894881439961679   UNAVAIL      0     0     0  was /dev/xvdb1
            12684627022060038255  UNAVAIL      0     0     0  was /dev/xvdd1
            4058956205729958166   UNAVAIL      0     0     0  was /dev/xvde1
            xvdf                  ONLINE       0     0     0

And noticed with just one remaining Cloud block storage device I was still able to access the data on the disk as well as create data:

cat file.txt  | tail
Testing. 135953
Testing. 135954
Testing. 135955
Testing. 135956
Testing. 135957
Testing. 135958
Testing. 135959
Testing. 135960
Testing. 135961
Testing. 135962

# mkdir test
root@zfs-noraid-testing:/noraidpool# ls -a
.  ..  ddfile  file.txt  forktest.sh  stat.sh  test  writetest.sh

That’s pretty flexible.