ZFS has combined volume manager and filesystem with several advanced features.
This is the first part in a series of articles on ZFS.
In the article, we’ll provide an high level introduction to ZFS, explain how to install ZFS on linux, create a ZFS pool, and several ZFS zpool commands.
1. Introduction to ZFS
The following are some of the features of ZFS filesystem:
- Protection against data corruption
- Support for high storage capacities
- Efficient data compression
- Take Snapshots of filesystem
- Copy-on-write clones
- RAID Z Support
- Integrity checking
- Automatic repair and support for native NFSV4 ACL
This was developed originally by Sun Microsystems for the Solaris platform. In 2010, Oracle acquired Sun microsystems and has made lot of improvements on ZFS filesystem.
ZFS is recently becoming popular on Linux as it has become more stable.
The ZFS on Linux port is produced by the Lawrence Livermore National Laboratory (LLNL).
ZFS on Linux is a kernel module that you can download, compile and install. You do not have to patch or recompile your kernel.
You can download the source packages for your respective OS distribution from here.
2. Install ZFS on Linux
In this article, we’ll be installing ZFS on CentOS server. But, the zfs commands mentioned below are same for almost all the distributions on Linux distros except the installation part.
Execute the following yum commands to install ZFS on Redhat / CentOS.
# yum localinstall --nogpgcheck https://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm # yum localinstall --nogpgcheck http://archive.zfsonlinux.org/epel/zfs-release.el6.noarch.rpm # yum install kernel-devel zfs
Please ensure all the dependencies are met. One of the dependencies where the installation normally fails, would be a requirement to install GCC compiler. In this case, please install the GCC compiler before installing ZFS.
Ensure that the ZFS modules are loaded us lsmod command as shown below:
# lsmod | grep zfs zfs 1188621 0 zcommon 45591 1 zfs znvpair 81046 2 zfs,zcommon zavl 6900 1 zfs zunicode 323051 1 zfs spl 264548 5 zfs,zcommon,znvpair,zavl,zunicode
On a related note, you may want to read about the basics on how Linux Loadable Kernel Modules are created.
We have added few disks on this server (/dev/sdb through /dev/sdf) to test the ZFS functionality.
# ls -l /dev/sd* brw-rw----. 1 root disk 8, 0 Jul 15 15:52 /dev/sda brw-rw----. 1 root disk 8, 1 Jul 15 15:52 /dev/sda1 brw-rw----. 1 root disk 8, 2 Jul 15 15:52 /dev/sda2 brw-rw----. 1 root disk 8, 3 Jul 15 15:52 /dev/sda3 brw-rw----. 1 root disk 8, 16 Jul 16 10:57 /dev/sdb brw-rw----. 1 root disk 8, 32 Jul 16 10:57 /dev/sdc brw-rw----. 1 root disk 8, 48 Jul 16 10:58 /dev/sdd brw-rw----. 1 root disk 8, 64 Jul 16 11:27 /dev/sde brw-rw----. 1 root disk 8, 80 Jul 16 11:27 /dev/sdf
3. Create a zpool
Zpool command used to configure the storage pools in ZFS. Storage pool is a collection of devices that provides physical storage and data replication for zfs datasets.
The following creates a zpool.
# zpool create -f mypool raidz sdb sdc sdd sde sdf
In the above example:
- create stands for creating a new pool.
- The -f option is to ignore disk partition labels since these are new disks
- raidz is raid level. RAIDZ is nothing but the variation of RAID-5 that allows for better distribute on of parity and eliminates the “RAID-5” write hole (data and parity inconsistency after a power loss).
- A raidz group can have single, double or tribe parity meaning it can sustain one, two, or three failures respectively without losing any data. Data and parity is striped across all disks within a raidz group.
Next, verify the status of the zpool that we just created.
# zpool status pool: mypool state: ONLINE scan: none requested config: NAME STATE READ WRITE CKSUM mypool ONLINE 0 0 0 raidz1-0 ONLINE 0 0 0 sdb ONLINE 0 0 0 sdc ONLINE 0 0 0 sdd ONLINE 0 0 0 sde ONLINE 0 0 0 sdf ONLINE 0 0 0 errors: No known data errors
Once the pool is created, if you do df –h, you will see the newly created pool is mounted automatically on the mountpount.
# df -h Filesystem Size Used Avail Use% Mounted on /dev/mapper/vglocal-rootlv 14G 2.4G 11G 18% / tmpfs 939M 0 939M 0% /dev/shm /dev/sda1 504M 46M 433M 10% /boot mypool 3.9G 0 3.9G 0% /mypool
4. Create a Mirrored Pool
To create a mirrored pool, uze the zpool create command with the following options.
If any of the disk in the particular mirror group is failed, then the other disk still holds the data. As soon as the failed disk is replaced the contents are mirrored back(also known as resilvering) to the newly replaced disk.
# zpool create -f mypool mirror sdb sdc mirror sdd sde
Next, verify the status of the mirrored zpool that we just created:
# zpool status -v pool: mypool state: ONLINE scan: none requested config: NAME STATE READ WRITE CKSUM mypool ONLINE 0 0 0 mirror-0 ONLINE 0 0 0 sdb ONLINE 0 0 0 sdc ONLINE 0 0 0 mirror-1 ONLINE 0 0 0 sdd ONLINE 0 0 0 sde ONLINE 0 0 0 errors: No known data errors
5. Zpool Import and Export
There are some cases when you may need to migrate a zfs pools between systems.
ZFS makes this possible by exporting a pool from one system and importing it to another system.
To export any pool, use the zpool export command and zpool import command is used to import the pool as shown in the following example:
# zpool export mypool # zpool import mypool
6. View I/O stats of the ZFS Pool
To view the zpool I/O statistics, use the zpool iostat command as shown below:
# zpool iostat -v mypool capacity operations bandwidth pool alloc free read write read write ---------- ----- ----- ----- ----- ----- ----- mypool 147K 4.95G 0 0 33 252 mirror 54K 3.97G 0 0 10 84 sdb - - 0 0 536 612 sdc - - 0 0 282 612 mirror 93K 1008M 0 0 23 168 sdd - - 0 0 288 696 sde - - 0 0 294 696 ---------- ----- ----- ----- ----- ----- -----
7. Delete a ZFS pool
To destroy a pool, use the zpool destroy command as shown below:
# zpool destroy mypool
8. Replace Corrupted disk in ZFS pool
To replace a disk, after a failure or corruption, use the following command:
# zpool replace mypool sde sdf
9. Expand ZFS Pool with new Disk
To expand the zpool by adding a new disk use the zpool command as given below:
# zpool add -f mypool sde
10. Add a Spare Disk to ZFS Pool
You can also add a spare disk to the zfs pool using the below command, by adding a spare device to a zfs pool.
The failed disks is automatically replaced by the spare device and administrator can replace the failed disks at later time.
Please note that you can also share the spare device among multiple ZFS pools.
# zpool add -f mypool spare sde
In the next part of the article, we’ll explain how to use the ZFS pools to create ZFS filesystem, mount the ZFS filesystem, and manipulate it from the command line.