A Must-Read for Linux Users: Easily Create an Efficient ZFS File System with File Compression

Abstract: The ZFS file system has gained wider recognition on Linux. In ZFS, you can enable compression at the file system level. This will store data in a compressed format, saving a significant amount of disk space. In this article, we will explain how to create a file system from a ZFS storage pool and enable compression on ZFS.

The ZFS file system has gained wider recognition on Linux.

In ZFS, you can enable compression at the file system level. This will store data in a compressed format, saving a significant amount of disk space.

In this article, we will explain how to create a file system from a ZFS storage pool and enable compression on ZFS.

In the first part of this series, we explained the basics of ZFS and how to install ZFS on Linux. We also created a ZFS pool.

Creating a ZFS File System

First, use the zfs list command to view all current ZFS file systems, as shown below. In this example, we currently have one ZFS file system.

# zfs list
NAME         USED  AVAIL  REFER  MOUNTPOINT
mypool       170K  5.84G    30K  /mypool
mypool/fs1    30K  5.84G    30K  /mypool/fs1

Now, use the zfs create command to create a new ZFS file system.

# zfs set quota=1G mypool/fs1

As shown below, the new ZFS file system has been successfully created.

# zfs list
NAME         USED  AVAIL  REFER  MOUNTPOINT
mypool       170K  5.84G    30K  /mypool
mypool/fs1    30K  5.84G    30K  /mypool/fs1

Setting ZFS Quota and Reservation

When creating a ZFS file system, it will, by default, consume all space in the pool. Therefore, you must specify a quota and reservation for the file system.

To set the quota, use the zfs set command as shown below. Here, we specify the quota for this file system as 1GB.

# zfs set quota=1G mypool/fs1

Next, set the reservation for the file system. In this example, fs1 has reserved 256M out of 5.59G, so no one can use this space, and it can expand to 1G based on the quota we set if there is available space.

# zfs set reservation=256M mypool/fs1

# zfs list
NAME         USED  AVAIL  REFER  MOUNTPOINT
mypool       256M  5.59G  32.5K  /mypool
mypool/fs1    30K  1024M    30K  /mypool/fs1

Creating an Alternative Mount Point for ZFS

In addition to using the name mypool/fs1 to mount it, you can set an alternative mount point with any name you wish for the file system.

For example, the following command sets the mount point to /testmnt instead of mypool/fs1.

# zfs set mountpoint=/testmnt mypool/fs1

As we can see from the output below, the first column NAME indicates the real name of the ZFS file system. The last column MOUNTPOINT indicates the alternative mount point we created above.

# zfs list
NAME         USED  AVAIL  REFER  MOUNTPOINT
mypool       256M  5.59G  32.5K  /mypool
mypool/fs1    30K  1024M    30K  /testmnt

When you execute the df command, you will see the alternative mount point as shown below.

# df -h
Filesystem                  Size  Used Avail Use% Mounted on
..
mypool                      5.6G  128K  5.6G   1% /mypool
mypool/fs1                  1.0G  128K  1.0G   1% /testmnt

Enabling Compression on the ZFS File System

To set compression on a ZFS dataset, you can set the compression property as shown below. Once this property is set, all large files stored on this ZFS file system will be compressed.

# zfs set compression=lzjb mypool/fs1

The following are valid compression properties:

on
off
lzjb
gzip
gzip[1-9]
zle

You can also enable compression on an existing file system. In this case, compression will only apply to new and modified data; any existing data will remain uncompressed.

Verifying ZFS Compression

In the following example, we have copied a 61M tar file to the ZFS file system mypool/fs1 mounted at /testmnt.

# ls -lh /testmnt/test.tar
-rw-r--r--. 1 root root 61M Nov 11 09:44 /testmnt/test.tar

If you check the total size of the USED space from the zfs list command, you will see that only 20.9M of space is consumed, indicating that compression is enabled and working.

# zfs list
NAME         USED  AVAIL  REFER  MOUNTPOINT
mypool       256M  5.59G  32.5K  /mypool
mypool/fs1  20.9M  1003M  20.9M  /testmnt

You can also use the following command to get the compression ratio.

# zfs get compressratio mypool/fs1
NAME        PROPERTY       VALUE  SOURCE
mypool/fs1  compressratio  2.90x  -

In addition to compression, the ZFS file system has several advanced features. In the next article of the ZFS series, we will discuss how to obtain ZFS clones and snapshots.

Link: https://bbs.huaweicloud.com/blogs/379559

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