How many of you would love to use ZFS on linux for its excellent snapshot features, but cannot? How about we setup a FreeBSD host with ZFS, then on linux we mount the ZFS as ISCSI, format it as ext4 then we can snapshot that partition anytime we want and roll it back anytime we want? I have been using FreeBSD for years on ZFS with over 10TB of data, its very stable on this OS, let’s see how I’d go about accomplishing keeping ZFS for backup snapshots:

#ISCSI
#Freebsd- Lets Setup Server Portion Of ISCSI:
#notice how df will not show data/iscsitest, as we creating a block device
zfs destroy data/iscsitest
zfs create -V 20G data/iscsitest
zfs list -o name,used,avail,volsize
cd /usr/ports/net/istgt; make install
cd /usr/local/etc/istgt/
cp auth.conf.sample auth.conf
cp istgt.conf.sample istgt.conf
cp istgtcontrol.conf.sample istgtcontrol.conf
pico istgt.conf
[PortalGroup1]
…
Portal DA1 192.168.0.3:3269 …

[InitiatorGroup1]
…
Netmask 192.168.0.0/24 …

[LogicalUnit1]
…
LUN0 Storage /dev/zvol/data/iscsitest Auto
…

/usr/local/etc/rc.d/istgt start

#Linux:
yum install iscsi-initiator-utils
service iscsi start
iscsiadm -m discovery -t sendtargets -p 192.168.0.3
fdisk -l(find the new device…perhaps it is /dev/sdf)
gdisk /dev/sdf (partition it…maybe sdf1 as ext4)
mkfs.ext4 /dev/sdf1
mkdir /mnt; mount -t ext4 /dev/sdf1 /mnt
(toss in /etc/fstab if you like as: /dev/sdf1 /mnt ext4 _netdev 0 0) #notice the _netdev option is needed
chkconfig iscsi on

#OPTIONAL: How would we change size of partition?: (can delete old targets with : iscsiadm -m node -p 192.168.0.3 –op=delete)
Freebsd:
zfs set volsize=40G data/iscsitest
zfs list -o name,volsize
/usr/local/etc/rc.d/istgt restart
Linux:
(umount any iscsi partitions)
service iscsi restart
fdisk -l (check what /dev/sdaX it is and new size to confirm)
gdisk /dev/sdf (delete all partitions and save)
gdisk /dev/sdf (recreate it with max size and save)
resize2fs /dev/sdf1
(go ahead and mount it again, should have new size)

#FreeBSD snapshot test:
zfs snapshot data/iscsitest@test

(now time goes on and data gets written to /mnt on linux box, but something happens and we want to roll back)

#rollback:
Freebsd:
/usr/local/etc/rc.d/istgt stop
zfs rollback data/iscsitest@test
/usr/local/etc/rc.d/istgt start

Linux:
umount /mnt
mount /mnt (should be recovered)

#make your life easier crontab the snapshots Daily and Monthly:
21 4 * * * (/usr/local/etc/rc.d/istgt stop; zfs destroy data/iscsitest@`/bin/date +\%A`; zfs snapshot data/iscsitest@`/bin/date +\%A`; /usr/local/etc/rc.d/istgt start) > /dev/null 2>&1
0 0 1 * * (/usr/local/etc/rc.d/istgt stop; zfs destroy data/iscsitest@`/bin/date +\%B`; zfs snapshot data/iscsitest@`/bin/date +\%B`; /usr/local/etc/rc.d/istgt start) > /dev/null 2>&1

Until next time,

Dan.