One cool ZFS feature that was introduced in Solaris 10 11/06 is the ability to clone a file system. This is a truly powerful tool, since it allows admins to create copies of file systems prior to performing upgrades, and a way to roll a file system back to a previous state (this provides a simple lightweight method to back out changes if upgrades go awry). To illustrated just how useful this is, let’s create a clone of the file system oradata. To clone oradata, we first need to take a sapshot of the oradata file system:
$ zfs snapshot striped/oradata@ordata_snap
Once a snapshot is created, the zfs utilities’ “clone” option can be used to create a clone of the file system from the snaphost we just created:
$ zfs clone striped/oradata@ordata_snap striped/oradata_clone
After the clone is created, it can be “promoted” to a file system with the zfs utilities’ “promote” option:
$ zfs promote striped/oradata_clone
If everything works correctly (which it should), the clone and the file system the clone was created from will appear in the df output:
$ df -h
Filesystem size used avail capacity Mounted on
/dev/dsk/c0d0s0 17G 2.9G 14G 18% /
/devices 0K 0K 0K 0% /devices
/dev 0K 0K 0K 0% /dev
ctfs 0K 0K 0K 0% /system/contract
proc 0K 0K 0K 0% /proc
mnttab 0K 0K 0K 0% /etc/mnttab
swap 1016M 768K 1015M 1% /etc/svc/volatile
objfs 0K 0K 0K 0% /system/object
/usr/lib/libc/libc_hwcap1.so.1
17G 2.9G 14G 18% /lib/libc.so.1
fd 0K 0K 0K 0% /dev/fd
swap 1015M 0K 1015M 0% /tmp
swap 1015M 24K 1015M 1% /var/run
striped 52G 27K 50G 1% /striped
striped/oradata 52G 300M 50G 1% /striped/oradata
striped/oradata_clone
52G 300M 50G 1% /striped/oradata_clone
Now let’s pretend that a DBA accidentally deletes the Oracle datafiles in /striped/oradata:
$ rm -f /striped/oradata/*
Oops! Since oradata_clone is a clone of the oradata file system, we can restore oradata by first deleting the original file system (you could also rename it if you wanted to keep it around):
$ zfs destroy -f striped/oradata
And then renaming the clone to take it’s place:
$ zfs rename striped/oradata_clone striped/oradata
Once the rename occurs, everything is as it once was:
$ df -h
Filesystem size used avail capacity Mounted on
/dev/dsk/c0d0s0 17G 2.9G 14G 18% /
/devices 0K 0K 0K 0% /devices
/dev 0K 0K 0K 0% /dev
ctfs 0K 0K 0K 0% /system/contract
proc 0K 0K 0K 0% /proc
mnttab 0K 0K 0K 0% /etc/mnttab
swap 1015M 768K 1014M 1% /etc/svc/volatile
objfs 0K 0K 0K 0% /system/object
/usr/lib/libc/libc_hwcap1.so.1
17G 2.9G 14G 18% /lib/libc.so.1
fd 0K 0K 0K 0% /dev/fd
swap 1014M 0K 1014M 0% /tmp
swap 1014M 24K 1014M 1% /var/run
striped 52G 26K 50G 1% /striped
striped/oradata 52G 300M 50G 1% /striped/oradata
$ ls -la /striped/oradata
total 614555 drwxr-xr-x 2 root sys 5 Dec 24 11:49 . drwxr-xr-x 3 root sys 3 Dec 24 11:59 .. -rw-r--r-- 1 root root 104857600 Dec 24 11:47 iklts01.dbf -rw-r--r-- 1 root root 104857600 Dec 24 11:48 iklts02.dbf -rw-r--r-- 1 root root 104857600 Dec 24 11:49 iklts03.dbf
This has so many uses, and once ZFS boot is incorporated, using clones to protect yourself from rogue patches will be one of the coolest things ever! Shibby!