ZFS
This will be a quick overview on how to manage ZFS snapshots and volumes on a FreeBSD 9.0 system, but it should apply to Solaris as well.
A Few Assumptions
Suppose that my system has the following drives.
- ada0 WDC WD20EARS-00J99B0
- 3907029168 512 byte sectors
- ada2 WDC WD20EARS-00J99B0
- 3907029168 512 byte sectors
- ada3 ST2000DM001-9YN164
- 3907029168 512 byte sectors
- ada4 ST2000DL003-9VT166
- 3907029168 512 byte sectors
- ada5 ST2000DM001-9YN164
- 3907029168 512 byte sectors
Note: Find out what your disks are by running camcontrol devlist and fdisk
Creating a ZFS Volume
Since disk sizes may vary from one manufacturer to another, it's a good idea to not use the entire disk (See http://www.freebsddiary.org/zfs-with-gpart.php). Suppose that we want to put a 201MB buffer at the end of each disk, we would then need to do some calculations.
Convert 201 Megabytes into sectors: 201 Megabytes / 512 bytes / sector = 411648 sectors
Since our disks contains 3907029168 sectors, we would need to create a partition on each disk that has 3907029168 - 411648 (that is 3906617520) sectors. Please note that if you are using different disks with different sizes that you will need to adjust the calculation ( partition size = total sectors - 411648 ) accordingly.
# gpart add -b 2048 -s 3906617520 -t freebsd-zfs -l disk00 ada0 # gpart add -b 2048 -s 3906617520 -t freebsd-zfs -l disk01 ada2 # gpart add -b 2048 -s 3906617520 -t freebsd-zfs -l disk02 ada3 # gpart add -b 2048 -s 3906617520 -t freebsd-zfs -l disk03 ada4 # gpart add -b 2048 -s 3906617520 -t freebsd-zfs -l disk04 ada5
Once created, you should be able to create your new ZFS volume by running:
# zpool create -f storage raidz1 gpt/disk00 gpt/disk01 gpt/disk02 gpt/disk03 gpt/disk04
# zpool status
pool: storage
state: ONLINE
scan: none requested
config:
NAME STATE READ WRITE CKSUM
storage ONLINE 0 0 0
raidz1-0 ONLINE 0 0 0
gpt/disk00 ONLINE 0 0 0
gpt/disk01 ONLINE 0 0 0
gpt/disk02 ONLINE 0 0 0
gpt/disk03 ONLINE 0 0 0
gpt/disk04 ONLINE 0 0 0
errors: No known data errors
ZFS Snapshot
A ZFS snapshot is a read-only copy of the file system. It can be listed using the zfs list -t snapshot command.
# zfs list -t snapshot NAME USED AVAIL REFER MOUNTPOINT storage@20120820 31.4G - 3.21T - storage@20120924 134G - 4.15T - storage@20121028 36.2G - 4.26T - storage@20121201 33.2M - 4.55T -
To create a new snapshot, run
zfs snapshot storage@today
Note that this will not consume additional space when created. It will however grow in size when data gets modified.
# zfs list -t snapshot NAME USED AVAIL REFER MOUNTPOINT storage@20120820 31.4G - 3.21T - storage@20120924 134G - 4.15T - storage@20121028 36.2G - 4.26T - storage@20121201 33.2M - 4.55T - storage@today 0 - 4.58T -
Snapshot contents can be accessed through a special .zfs/snapshot/ directory. Each snapshot will contain a read-only copy of the data that existed when the snapshot was taken.
# ls /storage/.zfs/snapshot/ 20120820/ 20120924/ 20121028/ 20121201/ today/
To roll back to a specific snapshot, run zfs rollback storage@yesterday. This will restore your volume to the snapshot state.
# zfs rollback storage@yesterday
To delete a specific snapshot, run zfs destroy storage@today. Note that this will not work if other volumes depend on it. eg: If you cloned it as another volume.
# zfs destroy storage@today
Data Integrity
One of the strengths of ZFS its resiliency thanks to its transactional file system. The only way data stored on a ZFS volume to be in an inconsistent state is through hardware failure or some sort of fault with the ZFS implementation. Similar to a fsck on ext file systems, a ZFS scrub provides a way to perform filesystem checking. To initiate a scrub, run:
# zpool scrub storage
Once the scrub process is underway, you can view its status by running:
# zpool status storage
pool: storage
state: ONLINE
scan: scrub in progress since Mon Dec 3 23:54:53 2012
18.3G scanned out of 6.05T at 211M/s, 8h20m to go
0 repaired, 0.30% done
config:
NAME STATE READ WRITE CKSUM
storage ONLINE 0 0 0
raidz1-0 ONLINE 0 0 0
gpt/disk00 ONLINE 0 0 0
gpt/disk01 ONLINE 0 0 0
gpt/disk02 ONLINE 0 0 0
gpt/disk03 ONLINE 0 0 0
gpt/disk04 ONLINE 0 0 0
errors: No known data errors
To stop a scrub process, run:
# zpool scrub -s storage