The ZFS on Linux with FUSE
Using RAID
Listing 2 demonstrates a RAID-Z array with three (virtual) disks – RAID-Z2 is similar. (The keyword for RAID-Z2 is raidz2 instead of raidz.) The commands in Listing 2 create a pool with RAID functionality. Note that ZFS will not let you extend the capacity: You can't just add new disks to the RAID pool. However, there is a workaround. As shown in Listing 3, you can replace the existing disks with three larger disks.
Listing 2
RAID-Z
$ for i in $(seq 3); do dd if=/dev/zero of=/tmp/rpool$i bs=1024 count=65536; done $ zpool create rpool raidz /tmp/rpool1 /tmp/rpool2 /tmp/rpool3
Listing 3
Replacing the Disks
$ for i in $(seq 4 6); do dd if=/dev/zero of=/tmp/rpool$i bs=1024 count=128000; done $ zpool replace rpool /tmp/rpool1 /tmp/rpool4 $ zpool replace rpool /tmp/rpool2 /tmp/rpool5 $ zpool replace rpool /tmp/rpool3 /tmp/rpool6
Alternatively, you can increase the array capacity by adding mirror, or RAID-Z, pools to the existing pool, rpool (Listing 4). This technique makes sense when the new disks are the same size as the existing disks. As long as you have more than two disks, RAID-Z is preferable to mirroring for failure safety reasons.
Listing 4
Adding Pools
$ zpool add rpool mirror /tmp/rpool4 /tmp/rpool5 $ zpool add rpool raidz /tmp/rpool4 /tmp/rpool5 /tmp/rpool6
Preventing Data Loss
Modern hard disks have self-test functions that let you check current hardware status by running a special tool. If a disk is in a critical state, ZFS lets you remove it from the pool to check the hardware:
zpool offline rpool /tmp/rpool3
If you find out the hardware has an irreparable defect, you have no alternative but to replace it with the use of the zpool replace command, as shown in Listing 3. Whereas offline simply disables the disk in the array, the replace command swaps the existing medium.
ZFS then proceeds to synchronize the pool, which can take a couple of minutes. The zpool status command keeps you up to date with the current status.
If you are wondering why Apple is so interested in ZFS, you might consider an interesting feature in Mac OS X: The "Time Machine" stores filesystem states, which lets users restore older states. Time Machine is actually based on ZFS.
In OpenSolaris, the developers have integrated this feature with Nautilus [6]. On Linux, you currently have no alternative but to use the command line. To create a snapshot, type zfs snapshot rpool@created. The @ sign and an arbitrary string following it are important. The zfs list command outputs the existing pools and snapshots (Listing 5).
Listing 5
zlist Output
$ zfs list NAME USED AVAIL REFER MOUNTPOINT rpool 409K 266M 32,2K /rpool rpool@created 0 - 32,2K -
If you change a pool – that is, copy or add files – the USED and REFER columns will have changed from the original time. If you accidentally delete some data, zfs rollback rpool@created is all it takes to restore the pool to its original state.
Conclusions
Compared with the current crop of popular Linux filesystems, ZFS has some very interesting features, such as the integration of the Volume Manager and RAID and the ability to create snapshots. Other promising traits include online compression, or the ability to export or import pools. The many benefits of ZFS make it quite clear how big a lead this filesystem has over its competitors right now. Although Oracle's Btrfs promises similar abilities, it will take some time until it is ready for production use.
Infos
- ZFS: http://opensolaris.org/os/community/zfs/
- OpenSolaris: http://www.opensolaris.com
- Btrfs: http://btrfs.wiki.kernel.org/index.php/Main_Page
- FUSE: http://fuse.sourceforge.net/
- ZFS FUSE: https://developer.berlios.de/projects/zfs-fuse/
- Snapshot integration in Nautilus: http://blogs.sun.com/erwann/entry/zfs_on_the_desktop_zfs
« Previous 1 2
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
TUXEDO Computers Unveils Linux Laptop Featuring AMD Ryzen CPU
This latest release is the first laptop to include the new CPU from Ryzen and Linux preinstalled.
-
XZ Gets the All-Clear
The back door xz vulnerability has been officially reverted for Fedora 40 and versions 38 and 39 were never affected.
-
Canonical Collaborates with Qualcomm on New Venture
This new joint effort is geared toward bringing Ubuntu and Ubuntu Core to Qualcomm-powered devices.
-
Kodi 21.0 Open-Source Entertainment Hub Released
After a year of development, the award-winning Kodi cross-platform, media center software is now available with many new additions and improvements.
-
Linux Usage Increases in Two Key Areas
If market share is your thing, you'll be happy to know that Linux is on the rise in two areas that, if they keep climbing, could have serious meaning for Linux's future.
-
Vulnerability Discovered in xz Libraries
An urgent alert for Fedora 40 has been posted and users should pay attention.
-
Canonical Bumps LTS Support to 12 years
If you're worried that your Ubuntu LTS release won't be supported long enough to last, Canonical has a surprise for you in the form of 12 years of security coverage.
-
Fedora 40 Beta Released Soon
With the official release of Fedora 40 coming in April, it's almost time to download the beta and see what's new.
-
New Pentesting Distribution to Compete with Kali Linux
SnoopGod is now available for your testing needs
-
Juno Computers Launches Another Linux Laptop
If you're looking for a powerhouse laptop that runs Ubuntu, the Juno Computers Neptune 17 v6 should be on your radar.