ZFS within a Zone: Using Datasets
Posted on October 1, 2006
Around B43 Solaris Zones were given a new configuration attribute: dataset. This allows us to provide ZFS within a zone itself.
Before I continue, I think we should talk about ZFS terminology for a second. When I first started out with ZFS I found this idea of nested filesystems a bit odd. I remember watching the flash demo’s created by Dan Price and wondering why he kept creating filesystems within filesystems. When I see /storage/users/benr I think directories, not nested filesystems. But, over time as I’ve used ZFS more and more I’ve learned to adapt my thinking and now see the power and flexability provided. Instead of thinking of nested filesystems we can think of datasets within a pool which provide end-point filesystems. Of course to really see how this works you should sit down and look at the beauty of ZFS’s design (this is a good starting point, or listen to the designers describe in this video). And so for now, a pool is base structure that ties layout to disk, datasets are abstractions that act as a root for other filesystems, and filesystems are what you typically think of for storing data.
Back to the joys of ZFS… If your already using ZFS and Zones you have everything you need, you just need to connect the two. Lets see how.
Lets first take a look at the zone we’re going to modify using zonecfg‘s info option:
root@aeon ~$ zonecfg -z playzone001 info zonename: playzone001 zonepath: /ultrastor/playzone001 autoboot: true bootargs: pool: limitpriv: inherit-pkg-dir: dir: /lib inherit-pkg-dir: dir: /platform inherit-pkg-dir: dir: /sbin inherit-pkg-dir: dir: /usr net: address: 10.0.0.24 physical: nge0
As you can see, nothing special or interesting about it.
Now lets create a ZFS dataset, a filesystem that will host future filesystems within the zone:
root@aeon ~$ zfs create ultrastor/playzone001_ds
That was simple. Now lets give that dataset to the zone to use. We’ll use zonecfg to set the “dataset” resource’s “name” property which points to the dataset we just created. After making config change we’ll need to reboot the zone to make it take effect.
root@aeon ~$ zonecfg -z playzone001 'add dataset; set name="ultrastor/playzone001_ds"; end; verify; commit' root@aeon ~$ zoneadm -z playzone001 reboot
Done! Now lets have a looksie…
root@aeon ~$ zlogin playzone001 [Connected to zone 'playzone001' pts/15] Last login: Sat Sep 30 02:07:13 on pts/21 Sun Microsystems Inc. SunOS 5.11 snv_47 October 2007 # zfs list NAME USED AVAIL REFER MOUNTPOINT ultrastor 251G 115G 66.3G /ultrastor ultrastor/playzone001_ds 24.5K 115G 24.5K /ultrastor/playzone001_ds # df -h Filesystem size used avail capacity Mounted on ... ultrastor/playzone001_ds 366G 24K 115G 1% /ultrastor/playzone001_ds
Notice that its already mounted, but the mountpoint is ugly. Lets fix that and create a new filesystem.
# zfs set mountpoint=/zfs ultrastor/playzone001_ds # df -h Filesystem size used avail capacity Mounted on ... ultrastor/playzone001_ds 366G 24K 115G 1% /zfs # zfs create ultrastor/playzone001_ds/web # zfs set mountpoint=/web ultrastor/playzone001_ds/web # df -h /web Filesystem size used avail capacity Mounted on ultrastor/playzone001_ds/web 366G 24K 115G 1% /web # zfs snapshot ultrastor/playzone001_ds/web@snap1 # zfs list NAME USED AVAIL REFER MOUNTPOINT ultrastor 251G 115G 66.3G /ultrastor ultrastor/playzone001_ds 71.5K 115G 24.5K /zfs ultrastor/playzone001_ds/web 24.5K 115G 24.5K /web ultrastor/playzone001_ds/web@snap1 0 - 24.5K -
As you can see, using datasets within a zone is easy to do and adds a lot of power to your container deployments.
It should be noted… functionality within a zone isn’t prefect, for instance the pool and dataset isn’t hidden bellow the zone. It’d be nice ultimately to mask that somehow so you just saw “zfs” as the pool for instance. More noteworthy, however, zfs create -V (size) won’t work within the zone, it gets into a weird state where the filesystem is created but the size ignored, and then you can’t destroy it from within the zone, so you have to go back out to the globalzone and fix it there. But, thats pretty minor.