The zpool list command provides a number of ways to request information regarding pool status. The information available generally falls into three categories: basic usage information, I/O statistics, and health status. All three types of storage pool information are covered in this section.
You can use the zpool list command to display basic information about pools.
With no arguments, the command displays all the fields for all pools on the system. For example:
# zpool list
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
tank 80.0G 22.3G 47.7G 28% ONLINE -
dozer 1.2T 384G 816G 32% ONLINE -
This output displays the following information:
NAME
The name of the pool.
SIZE
The total size of the pool, equal to the sum of the size of all top-level virtual devices.
USED
The amount of space allocated by all datasets and internal metadata. Note that this amount is different from the amount of space as reported at the file system level.
For more information about determining available file system space, see ZFS Space Accounting.
AVAILABLE
The amount of unallocated space in the pool.
CAPACITY (CAP)The amount of space used, expressed as a percentage of total space.
HEALTH
The current health status of the pool.
For more information about pool health, see Health Status of ZFS Storage Pools.
ALTROOT
The alternate root of the pool, if any.
For more information about alternate root pools, see ZFS Alternate Root Pools.
You can also gather statistics for a specific pool by specifying the pool name. For example:
# zpool list tank
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
tank 80.0G 22.3G 47.7G 28% ONLINE -
Specific statistics can be requested by using the
o option.
This option allows for custom reports or a quick way to list pertinent information.
For example, to list only the name and size of each pool, you use the following
syntax:
# zpool list -o name,size
NAME SIZE
tank 80.0G
dozer 1.2T
The column names correspond to the properties that are listed in Listing Information About All Storage Pools.
The default output for the zpool list command is
designed for readability, and is not easy to use as part of a shell script.
To aid programmatic uses of the command, the
H option can
be used to suppress the column headings and separate fields by tabs, rather
than by spaces. For example, to request a simple list of all pool names on
the system:
# zpool list -Ho name
tank
dozer
Here is another example:
# zpool list -H -o name,size
tank 80.0G
dozer 1.2T
To request I/O statistics for a pool or specific virtual devices, use the zpool iostat command. Similar to the iostat command, this command can display a static snapshot of all I/O activity so far, as well as updated statistics for every specified interval. The following statistics are reported:
USED CAPACITY
The amount of data currently stored in the pool or device. This figure differs from the amount of space available to actual file systems by a small amount due to internal implementation details.
For more information about the difference between pool space and dataset space, see ZFS Space Accounting.
AVAILABLE CAPACITY
The amount of space available in the pool or device. As with
the used statistic, this is differs from the amount of
space available to datasets by a small margin.
READ OPERATIONS
The number of read I/O operations sent to the pool or device, including metadata requests.
WRITE OPERATIONS
The number of write I/O operations sent to the pool or device.
READ BANDWIDTH
The bandwidth of all read operations (including metadata), expressed as units per second.
WRITE BANDWIDTH
The bandwidth of all write operations, expressed as units per second.
With no options, the zpool iostat command displays the accumulated statistics since boot for all pools on the system. For example:
# zpool iostat
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
tank 100G 20.0G 1.2M 102K 1.2M 3.45K
dozer 12.3G 67.7G 132K 15.2K 32.1K 1.20K
Because these statistics are cumulative since boot, bandwidth might appear low if the pool is relatively idle. You can request a more accurate view of current bandwidth usage by specifying an interval. For example:
# zpool iostat tank 2
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
tank 100G 20.0G 1.2M 102K 1.2M 3.45K
tank 100G 20.0G 134 0 1.34K 0
tank 100G 20.0G 94 342 1.06K 4.1M
In this example, the command displays usage statistics only for the
pool tank every two seconds until the you type Ctrl-C.
Alternately, you can specify an additional count parameter,
which causes the command to terminate after the specified number of iterations.
For example, zpool iostat 2 3 would print a summary every
two seconds for three iterations, for a total of six seconds. If there is
a single pool, then the statistics is displayed on consecutive lines. If more
than one pool exists, then an additional dashed line delineates each iteration
to provide visual separation.
In addition to pool-wide I/O statistics, the zpool iostat command can display statistics for specific virtual devices. This command can be used to identify abnormally slow devices, or simply to observe the distribution of I/O generated by ZFS. To request the complete virtual device layout as well as all I/O statistics, use the zpool iostat -v command. For example:
# zpool iostat -v
capacity operations bandwidth
tank used avail read write read write
---------- ----- ----- ----- ----- ----- -----
mirror 20.4G 59.6G 0 22 0 6.00K
c1t0d0 - - 1 295 11.2K 148K
c1t1d0 - - 1 299 11.2K 148K
---------- ----- ----- ----- ----- ----- -----
total 24.5K 149M 0 22 0 6.00K
Note two important things when viewing I/O statistics on a virtual device basis.
First, space usage is only available for top-level virtual devices. The way in which space is allocated among mirror and RAID-Z virtual devices is particular to the implementation and not easily expressed as a single number.
Second, the numbers might not add up exactly as you would expect them to. In particular, operations across RAID-Z and mirrored devices will not be exactly equal. This difference is particularly noticeable immediately after a pool is created, as a significant amount of I/O is done directly to the disks as part of pool creation that is not accounted for at the mirror level. Over time, these numbers should gradually equalize, although broken, unresponsive, or offlined devices can affect this symmetry as well.
You can use the same set of options (interval and count) when examining virtual device statistics.
ZFS provides an integrated method of examining pool and device health. The health of a pool is determined from the state of all its devices. This state information is displaying by using the zpool status command. In addition, potential pool and device failures are reported by fmd and are displayed on the system console and the /var/adm/messages file. This section describes how to determine pool and device health. This chapter does not document how to repair or recover from unhealthy pools. For more information on troubleshooting and data recovery, see Chapter 9, ZFS Troubleshooting and Data Recovery.
Each device can fall into one of the following states:
ONLINE
The device is in normal working order. While some transient errors might still occur, the device is otherwise in working order.
DEGRADED
The virtual device has experienced failure but is still able to function. This state is most common when a mirror or RAID-Z device has lost one or more constituent devices. The fault tolerance of the pool might be compromised, as a subsequent fault in another device might be unrecoverable.
FAULTED
The virtual device is completely inaccessible. This status typically indicates total failure of the device, such that ZFS is incapable of sending or receiving data from it. If a top-level virtual device is in this state, then the pool is completely inaccessible.
OFFLINE
The virtual device has been explicitly taken offline by the administrator.
UNAVAILABLE
The device or virtual device cannot be opened. In some cases,
pools with UNAVAILABLE devices appear in DEGRADED mode.
If a top-level virtual device is unavailable, then nothing in the pool can
be accessed.
The health of a pool is determined from the health of all its top-level
virtual devices. If all virtual devices are ONLINE, then
the pool is also ONLINE. If any one of the virtual devices
is DEGRADED or UNAVAILABLE, then the
pool is also DEGRADED. If a top-level virtual device is FAULTED or OFFLINE, then the pool is also FAULTED. A pool in the faulted state is completely inaccessible. No data
can be recovered until the necessary devices are attached or repaired. A pool
in the degraded state continues to run, but you might not achieve the same
level of data replication or data throughput if the pool were online.
The simplest way to request a quick overview of pool health status is to use the zpool status command:
# zpool status -x
all pools are healthy
Specific pools can be examined by specifying a pool name to the command.
Any pool that is not in the ONLINE state should be investigated
for potential problems, as described in the next section.
You can request a more detailed health summary by using the
v option.
For example:
# zpool status -v tank
pool: tank
state: DEGRADED
status: One or more devices could not be opened. Sufficient replicas exist
for the pool to continue functioning in a degraded state.
action: Attach the missing device and online it using 'zpool online'.
see: http://www.sun.com/msg/ZFS-8000-2Q
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
tank DEGRADED 0 0 0
mirror DEGRADED 0 0 0
c1t0d0 FAULTED 0 0 0 cannot open
c1t1d0 ONLINE 0 0 0
errors: No known data errors
This output displays a complete description of why the pool is in its current state, including a readable description of the problem and a link to a knowledge article for more information. Each knowledge article provides up-to-date information on the best way to recover from your current problem. Using the detailed configuration information, you should be able to determine which device is damaged and how to repair the pool.
In the above example, the faulted device should be replaced. After the device is replaced, use the zpool online command to bring the device back online. For example:
#zpool online tank c1t0d0Bringing device c1t0d0 online #zpool status -xall pools are healthy
If a pool has an offlined device, the command output identifies the problem pool. For example:
# zpool status -x
pool: tank
state: DEGRADED
status: One or more devices could not be opened. Sufficient replicas exist for
the pool to continue functioning in a degraded state.
action: Attach the missing device and online it using 'zpool online'.
see: http://www.sun.com/msg/ZFS-8000-D3
scrub: resilver completed with 0 errors on Fri Mar 17 14:38:47 2006
config:
NAME STATE READ WRITE CKSUM
tank DEGRADED 0 0 0
mirror DEGRADED 0 0 0
c1t0d0 UNAVAIL 0 0 0 cannot open
c1t1d0 ONLINE 0 0 0
The READ and WRITE columns provides
a count of I/O errors seen on the device, while the CKSUM column
provides a count of uncorrectable checksum errors that occurred on the device.
Both of these error counts likely indicate potential device failure, and some
corrective action is needed. If non-zero errors are reported for a top-level
virtual device, portions of your data might have become inaccessible. The
errors count identifies any known data errors.
In the example output above, the offlined device is not causing data errors.
For more information about diagnosing and repairing faulted pools and data, see Chapter 9, ZFS Troubleshooting and Data Recovery.