To use and config zfs, you need to create at least one zpool first.
After that, you should have something like this:
# zpool list
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
zfstest 23.8G 91K 23.8G 0% ONLINE -
This zpool “zfstest” also has one incorporated zfs filesystem on it. To manipulate zfs there is the “zfs” command. So keep in mind: zpool manipulates pool storage, zfs manipulates zfs generation and options. Try this:
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfstest 88K 23.4G 24.5K /zfstest
As you can see, the pool “zfstest” also has a filesystem on it, mounted automatically at mountpoint /zfstest.
You may create a new filesystem by using “zfs create”:
# zfs create zfstest/king
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfstest 118K 23.4G 25.5K /zfstest
zfstest/king 24.5K 23.4G 24.5K /zfstest/king
New filesystems within a pool are always named “poolname/filesystemname”. Without any additional options, it will also mount automatically on “/poolname/filesystemname”. Let’s create another one:
# zfs create zfstest/queen
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfstest 147K 23.4G 25.5K /zfstest
zfstest/king 24.5K 23.4G 24.5K /zfstest/king
zfstest/queen 24.5K 23.4G 24.5K /zfstest/queen
We see some differences between old-fashioned filesystems and zfs: Usable storage is shared among all filesystems in a pool. “zfstest/king” has 23.4G available, “zfstest/queen” also, as does the master pool filesystem “zfstest”.
So why create filesystems then? Couldn’t we just use subdirectories in our master pool filesystem “zfstest” (mounted on /zfstest)?
The “trick” about zfs filesystems is the possibility to assign options to them, so they can be treated differently. We will see that later.
First, let’s push some senseless data on our newly created filesystem:
# dd if=/dev/zero bs=128k count=5000 of=/zfstest/king/bigfile
5000+0 records in
5000+0 records out
This command creates a file “bigfile” in directory /zfstest/king, consisting of 5000 times 128 kilobytes. That’s big enough for our purpose.
”zfs list” reads:
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfstest 625M 22.8G 27.5K /zfstest
zfstest/king 625M 22.8G 625M /zfstest/king
zfstest/queen 24.5K 22.8G 24.5K /zfstest/queen
625 megabytes are used from filesystem zfstest/king, as expected. Notice also that now every other filesystem on that pool only can allocate 22.8G, as 625M are taken (compare with 23.4 G above, before creating that big file).
You CAN look up free space in your zfs filesystems also doing a “df -k”, but I wouldn’t recommend it: You won’t see snapshots and the numbers can be very big.
Example for our zpool “zfstest”:
# df -k
Filesystem kbytes used avail capacity Mounted on
/dev/dsk/c0d0s0 14951508 5725184 9076809 39% /
/devices 0 0 0 0% /devices
ctfs 0 0 0 0% /system/contract
[... lines omitted ...]
zfstest 24579072 27 23938789 1% /zfstest
zfstest/king 24579072 640149 23938789 3% /zfstest/king
zfstest/queen 24579072 24 23938789 1% /zfstest/queen
So 22.8G are 23938789 bytes. Sun uses 1K=1024 bytes, 1M = 1024K, 1G = 1024M, 1T = 1024G. They’re a computer company and not an ISO metric organization…
So let’s try out first option: “quota”.
As you can imagine, “quota” limits storage. You know that as nearly every mailbox provider do impose a quota on your storage, as do file space providers.
First: To set and get options, you need to use “zfs set” and “zfs get”, respectively.
So here we define a quota on zfstest/queen:
# zfs set quota=5G zfstest/queen
Result:
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfstest 625M 22.8G 27.5K /zfstest
zfstest/king 625M 22.8G 625M /zfstest/king
zfstest/queen 24.5K 5.00G 24.5K /zfstest/queen
Only 5G left to use at mountpoint /zfstest/queen. Note, that you may still gobble up 22.8G in /zfstest/king, making it impossible then to put 5G in /zfstest/queen. So a quota does not guarantee any storage, it only limits it.
To guarantee a certain amount of storage, use the option “reservation”:
# zfs set reservation=5G zfstest/queen
Now we simulated a classical “partition” – we reserved the same amount of storage as the quota implies, 5G:
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfstest 5.61G 17.8G 27.5K /zfstest
zfstest/king 625M 17.8G 625M /zfstest/king
zfstest/queen 24.5K 5.00G 24.5K /zfstest/queen
The other filesystems only have 17.8G left, as 5 G are really reserved for zfstest/queen.
Now, let’s try another nice option: compression
Perhaps now you are thinking about compression nightmares on windows systems, like doublespace, stacker and all these other parasital programs which killed performance, not storage. Forget them! zfs compression IS reliable and – fast!
With todays’ CPU power the effect of compressing and decompressing objects is a charm and won’t harm significantly your overall performance – it can boost performance as you will need less i/o due to compression.
As with many other zfs options, changing the compression only affects newly written files/sectors. Uncompressed blocks still can be read. It’s transparent to the application. fseek() et.al. do not even notice that files are compressed.
# zfs set compression=on zfstest/queen
Now, compression is activated on /zfstest/queen (as “zfstest/queen” is mounted on /zfstest/queen, we did not change the mountpoint – and yes, you’re right, the mountpoint is also just another zfs option…).
Let’s copy our “bigfile” from king to queen:
# cp /zfstest/king/bigfile /zfstest/queen
Ok THIS in unfair – as our file consists of only zeroes, zfs won’t compress it, it only sets up a marker saying that 655360000 bytes of zeroes have to be generated. It is some kind of “benchmark” hook to get nice results and to avoid to waste space with “hole files”:
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfstest 5.61G 17.8G 27.5K /zfstest
zfstest/king 625M 17.8G 625M /zfstest/king
zfstest/queen 24.5K 5.00G 24.5K /zfstest/queen
No space needed in zfstest/queen… You may check it with “ls -las” (option “s” prints out the number of needed disk blocks to store the file):
# ls -las /zfstest/queen
total 7
3 drwxr-xr-x 2 root sys 3 Apr 23 06:17 .
3 drwxr-xr-x 4 root sys 4 Apr 23 06:05 ..
1 -rw-r–r– 1 root root 655360000 Apr 23 06:18 bigfile
One block. On our uncompressed king filesystem the situation is like that:
# ls -las /zfstest/king
total 1280257
3 drwxr-xr-x 2 root sys 4 Apr 23 06:19 .
3 drwxr-xr-x 4 root sys 4 Apr 23 06:05 ..
1280251 -rw-r–r– 1 root root 655360000 Apr 23 06:10 bigfile
To be able to create a “real world” file, we will use the “zfs get all” command, to get ALL options of a zfs filesystem:
# zfs get all zfstest/queen
NAME PROPERTY VALUE SOURCE
zfstest/queen type filesystem -
zfstest/queen creation Wed Apr 23 6:05 2008 -
zfstest/queen used 24.5K -
zfstest/queen available 5.00G -
zfstest/queen referenced 24.5K -
zfstest/queen compressratio 1.00x -
zfstest/queen mounted yes -
zfstest/queen quota 5G local
zfstest/queen reservation 5G local
zfstest/queen recordsize 128K default
zfstest/queen mountpoint /zfstest/queen default
zfstest/queen sharenfs off default
zfstest/queen checksum on default
zfstest/queen compression on local
zfstest/queen atime on default
zfstest/queen devices on default
zfstest/queen exec on default
zfstest/queen setuid on default
zfstest/queen readonly off default
zfstest/queen zoned off default
zfstest/queen snapdir hidden default
zfstest/queen aclmode groupmask default
zfstest/queen aclinherit secure default
zfstest/queen canmount on default
zfstest/queen shareiscsi off default
zfstest/queen xattr on default
As you remark, the “compressratio” option (which is a read-only option, so you may only use “zfs get” and not “zfs set”) gives the compression ratio of your filesystem, but our “zero file” does not count, so it remains 1.00x!) . So let’s create another file now in your compressed queen filesystem:
# zfs get all zfstest/queen > /zfstest/queen/outputfile
Our file will use 3 disk blocks:
# ls -las /zfstest/queen
total 10
3 drwxr-xr-x 2 root sys 4 Apr 23 06:18 .
3 drwxr-xr-x 4 root sys 4 Apr 23 06:05 ..
1 -rw-r–r– 1 root root 655360000 Apr 23 06:18 bigfile
3 -rw-r–r– 1 root root 1598 Apr 23 06:18 outputfile
Let’s copy it to our uncompressed king filesystem:
# cp /zfstest/queen/outputfile /zfstest/king/
Here it will use 5 blocks:
# ls -las /zfstest/king
total 1280262
3 drwxr-xr-x 2 root sys 4 Apr 23 06:19 .
3 drwxr-xr-x 4 root sys 4 Apr 23 06:05 ..
1280251 -rw-r–r– 1 root root 655360000 Apr 23 06:10 bigfile
5 -rw-r–r– 1 root root 1598 Apr 23 06:19 outputfile
These were the basic steps to create zfs filesystems, but at least one command is missing: How do destroy filesystems? Use “zfs destroy”:
# zfs destroy zfstest/king
# zfs destroy zfstest/queen
Note, that the filesystem must not be in use, otherwise it won’t work (just like any unmount (umount) of a classical filesystem won’t work when it’s in use).
Note, you may NOT destroy “zfstest”, because that’s the master filesystem of your pool, destroy your pool if you want to get rid of it:
# zfs destroy zfstest
cannot destroy ‘zfstest’: operation does not apply to pools
use ‘zfs destroy -r zfstest’ to destroy all datasets in the pool
use ‘zpool destroy zfstest’ to destroy the pool itself
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