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This chapter is from the book

This chapter is from the book

2.3 Creating a Pool with Mirrored Devices

The following command creates a ZFS mirrored pool called mpool with a mirrored vdev. As expected, the new pool mpool is about half the capacity of dstripe. The pool dstripe is a concatenation of two disks of the same capacity, and mpool is a mirror of a disk of the same capacity.

The following command line shows how to use the zpool command with the subcommand create to create a pool with mirrored vdevs. After the create subcommand is the name of the new ZFS pool, mpool. The mirror subcommand will create a mirrored vdev with the disks c5t2d0 and c5t3d0.

# zpool create mpool mirror c5t2d0 c5t3d0

The following output is the creation of a mirrored ZFS pool called mpool. Using the zpool list command, you now can see the capacity of the newly created pool on line 5. Notice it is half the capacity of the dstripe pool.

1   # zpool create mpool mirror c5t2d0 c5t3d0
2   # zpool list
3   NAME      SIZE   USED  AVAIL    CAP  HEALTH  ALTROOT
4   dstripe   234M    75K   234M     0%  ONLINE  -
5   mpool     117M  73.5K   117M     0%  ONLINE  -
6   rpool    15.9G  3.21G  12.7G    20%  ONLINE  -

Starting at line 20 (in the following part of the listing) is the status information of mpool. The disks c5t2d0 and c5t3d0 are configured as a mirror vdev, and the mirror is part of mpool. This is an important concept in reading the status information of ZFS pools. Notice the indentations on the pool name notations. The first is the name of the ZFS pool. Then at the first indentation of the name are the vdevs that are part of the pool. In the case of a dynamic stripe, this is the physical device. If the pool is created with redundant vdev(s), the first indentation will be mirror, raidz1, or raidz2. Then the next indentation will be the physical devices that comprise the redundant vdev. On lines 13 and 25 are the names dstripe and mpool, respectively. On lines 14 and 15 are the disks that belong to dstripe on the first indentation. On line 25 is the mirror configuration, and the next indented line lists the disks belonging to the mirror configuration. Compare Figures 2.1 and 2.2 for a graphical representation of each pool's configuration.

Figure 2.2

Figure 2.2 Pool mpool with a mirrored vdev

7   # zpool status
8   pool: dstripe
9   state: ONLINE
10  scrub: none requested
11  config:
12
13         NAME        STATE      READ WRITE CKSUM
14         dstripe     ONLINE        0     0     0
15           c5t0d0    ONLINE        0     0     0
16           c5t1d0    ONLINE        0     0     0
17
18  errors: No known data errors
19
20    pool: mpool
21   state: ONLINE
22   scrub: none requested
23  config:
24          NAME        STATE      READ WRITE CKSUM
25          mpool       ONLINE        0     0     0
26            mirror    ONLINE        0     0     0
27              c5t2d0  ONLINE        0     0     0
28              c5t3d0  ONLINE        0     0     0
29
30  errors: No known data errors
31
32    pool: rpool
33   state: ONLINE
34   scrub: none requested
35  config:
36
37          NAME        STATE      READ WRITE CKSUM
38          rpool       ONLINE        0     0     0
39            c3d0s0    ONLINE        0     0     0
40  errors: No known data errors

Figure 2.2 illustrates the results of creating the ZFS pool mpool with one mirrored vdev.

The following sequence adds a second mirror vdev to the pool, doubling the size of pool mpool. Notice that after the addition of the second mirror vdev, the dstripe and mpool pools are the same capacity. Line 30 is the mirrored vdev with the physical disks c5t4d0 and c5t5d0 indented.

1.  # zpool add mpool mirror c5t4d0 c5t5d0
2.  # zpool list
3.  NAME      SIZE   USED  AVAIL    CAP  HEALTH  ALTROOT
4.  dstripe   234M    75K   234M     0%  ONLINE  -
5.  mpool     234M    78K   234M     0%  ONLINE  -
6.  rpool    15.9G  3.21G  12.7G    20%  ONLINE  -
7.  # zpool status
8.       pool: dstripe
9.      state: ONLINE
10.  scrub: none requested
11. config:
12.
13. NAME        STATE     READ WRITE CKSUM
14. dstripe     ONLINE       0     0     0
15.   c5t0d0    ONLINE       0     0     0
16.   c5t1d0    ONLINE       0     0     0
17.
18. errors: No known data errors
19.
20.   pool: mpool
21.  state: ONLINE
22.  scrub: none requested
23. config:
24.
25. NAME        STATE     READ WRITE CKSUM
26. mpool       ONLINE       0     0     0
27.   mirror    ONLINE       0     0     0
28.     c5t2d0  ONLINE       0     0     0
29.     c5t3d0  ONLINE       0     0     0
30.   mirror    ONLINE       0     0     0
31.     c5t4d0  ONLINE       0     0     0
32.     c5t5d0  ONLINE       0     0     0
33.
34. errors: No known data errors
35.
36.   pool: rpool
37.  state: ONLINE
38.  scrub: none requested
39. config:

40. NAME        STATE     READ WRITE CKSUM
41. rpool       ONLINE       0     0     0
42.   c3d0s0    ONLINE       0     0     0

43. errors: No known data errors

Figure 2.3 shows the results of adding a second mirrored vdev to ZFS pool mpool.

Figure 2.3

Figure 2.3 Pool mpool with the added mirror vdev

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