我之前运行的是 FreeBSD 10.0-RELEASE-p4，后来迁移到了 FreeBSD 版本的 NAS4Free 10.2-RELEASE #0 r286738M: Thu Aug 13 21:32:58 CEST 2015。现在我缺少可用空间，无法从池中删除任何文件。读取文件工作正常。
所有驱动器都是 2 TB。我忘记在迁移之前导出池。根据互联网来源，导出和导入池应该可以释放空间，但事实并非如此。池运行的是版本 15。升级或清理有帮助吗？
NAME STATE READ WRITE CKSUM
storage ONLINE 0 0 0
raidz2-0 ONLINE 0 0 0
da0 ONLINE 0 0 0 block size: 512B configured, 4096B native
da3 ONLINE 0 0 0 block size: 512B configured, 4096B native
da6 ONLINE 0 0 0 block size: 512B configured, 4096B native
da9 ONLINE 0 0 0 block size: 512B configured, 4096B native
da12 ONLINE 0 0 0 block size: 512B configured, 4096B native
da15 ONLINE 0 0 0 block size: 512B configured, 4096B native
raidz2-1 ONLINE 0 0 0
da1 ONLINE 0 0 0 block size: 512B configured, 4096B native
da4 ONLINE 0 0 0 block size: 512B configured, 4096B native
da7 ONLINE 0 0 0 block size: 512B configured, 4096B native
da10 ONLINE 0 0 0 block size: 512B configured, 4096B native
da13 ONLINE 0 0 0 block size: 512B configured, 4096B native
da16 ONLINE 0 0 0 block size: 512B configured, 4096B native
raidz2-2 ONLINE 0 0 0
da2 ONLINE 0 0 0 block size: 512B configured, 4096B native
da5 ONLINE 0 0 0 block size: 512B configured, 4096B native
da8 ONLINE 0 0 0 block size: 512B configured, 4096B native
da11 ONLINE 0 0 0 block size: 512B configured, 4096B native
da14 ONLINE 0 0 0 block size: 512B configured, 4096B native
da17 ONLINE 0 0 0 block size: 512B configured, 4096B native
所以：（（6 个驱动器 - 2 个驱动器用于奇偶校验）x 2 TB）x 3 raidz2 = 24 TB，即 21.83 太字节可用空间减去元数据。
特性：
# zpool get all
NAME PROPERTY VALUE SOURCE
storage size 32.6T -
storage capacity 97% -
storage altroot - default
storage health ONLINE -
storage guid 14393350251601347202 local
storage version 15 local
storage bootfs - default
storage delegation on default
storage autoreplace off default
storage cachefile - default
storage failmode wait default
storage listsnapshots off default
storage autoexpand off default
storage dedupditto 0 default
storage dedupratio 1.00x -
storage free 696G -
storage allocated 31.9T -
storage readonly off -
storage comment - default
storage expandsize - -
storage freeing 0 local
storage fragmentation - -
storage leaked 0 local
storage feature@async_destroy disabled local
storage feature@empty_bpobj disabled local
storage feature@lz4_compress disabled local
storage feature@multi_vdev_crash_dump disabled local
storage feature@spacemap_histogram disabled local
storage feature@enabled_txg disabled local
storage feature@hole_birth disabled local
storage feature@extensible_dataset disabled local
storage feature@embedded_data disabled local
storage feature@bookmarks disabled local
storage feature@filesystem_limits disabled local
storage feature@large_blocks disabled local
zpool iostat显示可用空间：
# zpool iostat -v
capacity operations bandwidth
pool alloc free read write read write
---------- ----- ----- ----- ----- ----- -----
storage 31.9T 696G 0 0 550 540
raidz2 10.8T 63.1G 0 0 162 2
da0 - - 0 0 185 135
da3 - - 0 0 157 135
da6 - - 0 0 158 135
da9 - - 0 0 163 135
da12 - - 0 0 158 135
da15 - - 0 0 149 135
raidz2 10.8T 90.1G 0 0 162 2
da1 - - 0 0 125 101
da4 - - 0 0 102 101
da7 - - 0 0 115 101
da10 - - 0 0 125 101
da13 - - 0 0 100 101
da16 - - 0 0 106 101
raidz2 10.3T 543G 0 0 225 536
da2 - - 0 0 139 243
da5 - - 0 0 133 244
da8 - - 0 0 118 246
da11 - - 0 0 123 246
da14 - - 0 0 123 244
da17 - - 0 0 124 243
---------- ----- ----- ----- ----- ----- -----
zpool list显示可用空间：
# zpool list storage
NAME SIZE ALLOC FREE EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
storage 32.6T 31.9T 696G - - 97% 1.00x ONLINE -
zfs list不显示可用空间：
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
storage 21.3T 0 21.3T /mnt/storage
df不显示可用空间：
# df -ha
Filesystem Size Used Avail Capacity Mounted on
/dev/xmd0 120M 69M 51M 58% /
devfs 1.0K 1.0K 0B 100% /dev
/dev/xmd1 719M 260M 459M 36% /usr/local
procfs 4.0K 4.0K 0B 100% /proc
storage 21T 21T 0B 100% /mnt/storage
/dev/xmd2 248M 3.9M 224M 2% /var
tmpfs 128M 48K 128M 0% /var/tmp
/dev/ada0s1a 743M 151M 592M 20% /cf
没有快照
# zfs list -t snapshot
no datasets available
数据集：
# zdb -d storage
Dataset mos [META], ID 0, cr_txg 4, 50.0M, 565 objects
Dataset storage [ZPL], ID 16, cr_txg 1, 21.3T, 1111968 objects
Verified large_blocks feature refcount is correct (0)
重复数据删除：
# zdb -D storage
All DDTs are empty
凸轮控制：
# camcontrol devlist -v
scbus0 on mpt0 bus 0:
<ATA SAMSUNG HD204UI 0001> at scbus0 target 0 lun 0 (pass0,da0)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 1 lun 0 (pass1,da1)
<ATA ST2000DM001-1CH1 CC43> at scbus0 target 2 lun 0 (pass2,da2)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 3 lun 0 (pass3,da3)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 4 lun 0 (pass4,da4)
<ATA ST2000DM001-1CH1 CC43> at scbus0 target 5 lun 0 (pass5,da5)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 6 lun 0 (pass6,da6)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 7 lun 0 (pass7,da7)
<ATA ST2000DM001-1CH1 CC43> at scbus0 target 8 lun 0 (pass8,da8)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 9 lun 0 (pass9,da9)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 10 lun 0 (pass10,da10)
<ATA ST2000DM001-1CH1 CC43> at scbus0 target 11 lun 0 (pass11,da11)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 12 lun 0 (pass12,da12)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 13 lun 0 (pass13,da13)
<ATA ST2000DM001-1CH1 CC43> at scbus0 target 14 lun 0 (pass14,da14)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 15 lun 0 (pass15,da15)
<ATA SAMSUNG HD204UI 0001> at scbus0 target 16 lun 0 (pass16,da16)
<ATA ST2000DM001-1CH1 CC43> at scbus0 target 17 lun 0 (pass17,da17)
<HP HP SAS EXP Card 2.06> at scbus0 target 18 lun 0 (pass18,ses0)
<> at scbus0 target -1 lun ffffffff ()
scbus1 on ata2 bus 0:
<> at scbus1 target -1 lun ffffffff ()
scbus2 on ata3 bus 0:
<> at scbus2 target -1 lun ffffffff ()
scbus3 on ata4 bus 0:
<KINGSTON SV300S37A60G 525ABBF0> at scbus3 target 0 lun 0 (ada0,pass19)
<> at scbus3 target -1 lun ffffffff ()
scbus4 on ata5 bus 0:
<> at scbus4 target -1 lun ffffffff ()
scbus-1 on xpt0 bus 0:
<> at scbus-1 target -1 lun ffffffff (xpt0)
答案1
FreeBSD 10.2 添加了可调参数，vfs.zfs.spa_slop_shift它控制默认保留多少空间。
来源：https://www.freebsd.org/releases/10.2R/relnotes.html#storage-zfs