When creating snapshot failed, the snapshot can not be deleted via GUI.
qm unlock <vm_id>Use snapshot name to create for each vm disk
zfs snapshot -r <disk_zvol>@<snapshot_name>There are many snapshots in Ubuntu system if using zfs as OS filesystem. In order to remove those old snapshots, need to list them by creation date using following command
zfs list -H -t snapshot -o name -S creationTo remove those old snapshots, for example, the oldest 18 snapshots can following command
zfs list -H -t snapshot -o name -S creation | tail -18 | xargs -n 1 zfs destroyGot two kind of messages of disk space issue on bpool.
ERROR couldn't save system state: Minimum free space to take a snapshot and preserve ZFS performance is 20%.
Free space on pool "bpool" is 19%.Add iSCSI LUN
Change grub configuration
Partition iSCSI LUN
Attach partitions into zpool
Detach old partitions from zpool
Repartition rpool and bpool partition in old disk
Add back to the rpool and bpool
Run update-grub2
Detach iSCSI rpool and bpool
Run following command to set autoexpand
zpool set autoexpand=on bpoolpartprobe or zfs onlinezpool online -e bpool <partition_id>zpool set autoexpand=off bpoolI also got unable to boot error due to removed local bpool, and grub can not find BOOT filesystem as it was in iSCSI LUN.
To fix this issue, use following steps
zfs import bpool to import bpool from iSCSIThis creates an issue, the two partitions has same blkid. After added the second iSCSI LUN.
HOWTO replace zfs bpool and rpool with larger disk - Ubuntu 20.04 (Virtualbox)
ZFS on Linux resize rpool
Storage provides are spinning disks or SSDs.
ls -al /dev/ada?Vdevs are grouping of storage providers into various RAID configurations.
Create stripes pool
zpool create OurFirstZpool ada1 ada2 ada3Create mirror vdev and add into pool
zpool create tank mirror ada1 ada2 ada3Create another group of mirror vdev and add into existing pool
zpool add tank mirror ada4 ada5 ada6Detach a disk from vdev
zpool detach tank ada4Create RAID-Z1 vdev and add into pool
zpool create tank raidz1 ada1 ada2 ada3Create a RAID-Z1 vdev and add into existing pool
zpool add tank raidz1 ada4 ada5 ada6Zpools are aggregation of vdevs into a single storage pools
Create pool
zpool create OurFirstZpool ada1 ada2 ada3Verify pool
zpool statusAdd a new disk (vdev) to increase space
zpool add OurFirstZpool ada4Z-Filesystems are datasets with cool features like compression and reservation.
Create dataset
zfs create OurFirstZpool/dataset1List dataset
zfs listAfter upgrade memory to 64GB, the memory usage is less than 32GB even run two VMs together. To utilize all memory, increase zfs cache size is one of the solution can be done.
The max arc size is defined as a module parameter, which can be viewed by following command
truenas# grep c_max /proc/spl/kstat/zfs/arcstats
c_max 4 62277025792
truenas# cat /sys/module/zfs/parameters/zfs_arc_max
62277025792
truenas#To justify this value, following command can be used, but it is not a persistent way.
echo 60129542144 > /sys/module/zfs/parameters/zfs_arc_maxMany suggestions can be found, some of them maybe workable, for example
echo "options zfs zfs_arc_max=34359738368" > /etc/modprobe.d/zfs.confBut they may not suitable for a NAS OS which can not be backed up using configuration backup provided by NAS OS.
Suggestion is update vfs.zfs.arc_max using sysctl, along with disable autotune, but it is only workable for kernel parameters, but no zfs parameters could be found, the zfs is loaded as module.
The parameter needs to be modified using TrueNAS web interface, to ensure that it will be saved during configuration export via System Settings => General => Manage Configuration => Download File.
So, following command is added into System Settings => Advanced => Init/Shutdown Scripts with When set to Post Init
echo 60129542144 > /sys/module/zfs/parameters/zfs_arc_maxVerify the setting as below.
arc_summary | grep sizeNote: The number is in bytes
In order to reduce the number without reboot, following command needs to be executed to reduce the cache immediately
echo 3 > /proc/sys/vm/drop_cachesWhy I cannot modify "vfs.zfs.arc_max" in WebUI?
QEMU / KVM: Using the Copy-On-Write mode
ZFS pool (Zpool) is a collection of one or more virtual devices (vdevs), vdev is a group of physical disks. They have following facts.
If there is a need to change the layout of the Zpool, the data should be backed up and the Zpool destroyed.
Datasets is the space emulating a regular file system.
Datasets can be nested, which can possess different settings for snapshots, compression, deduplication and so on.
Volumes (zvols) is the space emulating a block devices.
The copy-on-write mechanism is to keep old data on the disk.
Checksum information is written when data is written into disk, then verified when read data from disk. When checksum mismatch detected, use redundant data is used for correction.
Different checksum algorithms are used
RAID write hole in a RAID5/RAID1 occurs when one of the member disks doesn't match the others and by the nature of single-redundant RAID5/RAID1 it is impossible to tell which of the disks is bad.
ZFS is a self-healing system. If mismatched checksum is detected, ZFS tries to retrieve the data from other disks. If data correct, the system will amend the incorrect data and checksum.
If a disk in a Zpool fails, the pool is set to the degraded state, then data on the failed device is calculated and written to first the spare disk replaces the failed one. This is called resilvering. Once the restoration operation is complete, the status of the Zpool changes back to online. In case of when multiple disks have failed and if there are not enough redundant devices, the Zpool changes its state into unavailable.
In old system, export zpool, which unmounts Zpool’s datasets or zvols.
In new system, import zpool, which mount Zpool's datasets or zvols.
The scrubbing is consistency check operation, and try to repair corrupted data.
There is no online defragmentation in ZFS, so try to keep zpools below 70% utilization instead.
On ZFS, the data changes are stored on a different location than the original location on a disk and then the metadata is updated in that place on the disk. This mechanism guarantees that the old data is safely preserved in case of power loss or system crash that in other cases would result in loss of data.
The snapshot contains information about the original version of the file system to be retained. Snapshots do not require additional disk space within the pool. Once the data rendered in a snapshot is modified, the snapshot will take the disk space since it will now be pointing to the old data.
The clone is a writeable version of a snapshot. Overwriting the blocks in the cloned volume or file system results in decrementing the reference count on the previous block. The original snapshot that the clone is depending on, can not be deleted.
Rollback command is to go back to a previous version of a dataset or a volume. Note that the rollback command cannot revert changes from other snapshots than the most recent one. If to do so, all intermediate snapshots will be automatically destroyed.
Promote command is to replace an existing volume with its clone.
ZFS Essentials – What is pooled storage?
ZFS Essentials – Copy-on-write & snapshots
ZFS Essentials – Data integrity & RAIDZ
RAID Recovery Guide
There are two kinds of cache, read cache and write cache.
Called ARC and L2ARC.
In memory, caching the information that would require in the near future, while discarding the ones that will be needed furthest ahead in time.
This can be set using kernel/module parameter, such as zfs_arc_max.
In cache device, extension of ARC. Can be created using following command
zpool add tank cache ada3Note: tank is the pool name, ada3 is the block device used for caching
Called ZIL (ZFS Intent Log).
By default, ZFS will cache write data in memory before write to disk, this is called asynchronous mode.
Synchronous will make sure data written to disk before continue, this can be set using following command
zfs set sync=always mypool/dataset1This is the temporary space to store data before write into main disks, this can be used to speed up write operation. The write operation is considered as completed once data written into ZIL device, which is called SLOG (Separate Intent Log) devices, can be defined as follow
zpool add tank log ada3Note: tank is the pool name, ada3 is the block device used for slog
If worrying SLOG device faulty, it can be mirrored too.
zpool add tank log mirror ada3 ada4Configuring ZFS Cache for High Speed IO
ZFS Performance with Databases (Cached)
Following error was appearing in my dmesg monitoring screen.
txg_sync blocked for more than 120 seconds --> excessive loadIf I'm not wrong, it could be caused by slow harddisk speed, because the TrueNAS zfs cache is about 61GB, can take longer time to flush back to hard disk.
Same as other filesystem, zfs has writeback caching (aka write-behind caching), which will flush data back to hard disk in specific interval. zfs has synchronous and asynchronous mode, they are a bit different that readonly, writethrough and writeback mode.
Except above, zfs has different behaviors on copy on write (COW) as below.
Therefore, copy on write should be disabled for VM images. But if so, snapshot function could be lost.
Read-Through, Write-Through, Write-Behind Caching and Refresh-Ahead
There are so many snapshots when using zfs in ubuntu.
When tried to do release update, got following error
# do-release-update
...
...
Not enough free disk space
The upgrade has aborted. The upgrade needs a total of 256 M free
space on disk '/boot'. Please free at least an additional 91.4 M of
disk space on '/boot'. You can remove old kernels using 'sudo apt
autoremove' and you could also set COMPRESS=xz in
/etc/initramfs-tools/initramfs.conf to reduce the size of your
initramfs.
...This error messsage was occurred many times before, but those systems had very small /boot partition or many old kernels kept. If it is the first case, total repartitioning and moving root filesystem are required.
Examing disk space for bpool, found that zfs reported 675MB used in bpool, but actual usage is only 242MB.
root@ubuntu:~# zpool list
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
bpool 960M 675M 285M - - 30% 70% 1.00x ONLINE -
rpool 17.5G 7.99G 9.51G - - 21% 45% 1.00x ONLINE -
root@ubuntu:~# zfs list bpool
NAME USED AVAIL REFER MOUNTPOINT
bpool 675M 157M 96K /boot
root@ubuntu:~# du -cshx /boot
242M /boot
242M total
root@ubuntu:~# Then found many snapshots both in bpool and data pool
root@ubuntu:~# zfs list -t snapshot | head
NAME USED AVAIL REFER MOUNTPOINT
bpool/BOOT/ubuntu_e8m8h0@autozsys_ywm1ok 0B - 238M -
bpool/BOOT/ubuntu_e8m8h0@autozsys_ms74md 0B - 238M -
bpool/BOOT/ubuntu_e8m8h0@autozsys_ugu9z7 80K - 242M -
bpool/BOOT/ubuntu_e8m8h0@autozsys_r3xqau 72K - 242M -
bpool/BOOT/ubuntu_e8m8h0@autozsys_nkagbh 0B - 242M -
bpool/BOOT/ubuntu_e8m8h0@autozsys_xdbwsy 0B - 242M -
bpool/BOOT/ubuntu_e8m8h0@autozsys_zrt7vi 72K - 242M -
bpool/BOOT/ubuntu_e8m8h0@autozsys_jbmnwk 72K - 242M -
bpool/BOOT/ubuntu_e8m8h0@autozsys_0e5p2e 64K - 242M -
root@ubuntu:~#
root@ubuntu:~# zfs list -t snapshot | wc
301 1505 27701Too many! Not sure how many snapshots ubuntu likes to create
List all snapshots for /boot
root@ubuntu:~# df /boot
Filesystem 1K-blocks Used Available Use% Mounted on
bpool/BOOT/ubuntu_e8m8h0 408192 247808 160384 61% /boot
root@ubuntu:~# zfs list -H -o name -t snapshot bpool/BOOT/ubuntu_e8m8h0
bpool/BOOT/ubuntu_e8m8h0@autozsys_ywm1ok
bpool/BOOT/ubuntu_e8m8h0@autozsys_ms74md
bpool/BOOT/ubuntu_e8m8h0@autozsys_ugu9z7
bpool/BOOT/ubuntu_e8m8h0@autozsys_r3xqau
bpool/BOOT/ubuntu_e8m8h0@autozsys_nkagbh
bpool/BOOT/ubuntu_e8m8h0@autozsys_xdbwsy
bpool/BOOT/ubuntu_e8m8h0@autozsys_zrt7vi
bpool/BOOT/ubuntu_e8m8h0@autozsys_jbmnwk
bpool/BOOT/ubuntu_e8m8h0@autozsys_0e5p2e
bpool/BOOT/ubuntu_e8m8h0@autozsys_b17dwn
bpool/BOOT/ubuntu_e8m8h0@autozsys_uad1rb
bpool/BOOT/ubuntu_e8m8h0@autozsys_mxhvc9
bpool/BOOT/ubuntu_e8m8h0@autozsys_9athz8
bpool/BOOT/ubuntu_e8m8h0@autozsys_61umv1
bpool/BOOT/ubuntu_e8m8h0@autozsys_1q65cz
root@ubuntu:~# Then remove them
zfs list -H -o name -t snapshot bpool/BOOT/ubuntu_e8m8h0 | xargs -n 1 zfs destroyNow, it is ok to upgrade
root@ubuntu:~# zfs list -o space bpool
NAME AVAIL USED USEDSNAP USEDDS USEDREFRESERV USEDCHILD
bpool 589M 243M 0B 96K 0B 243M
root@ubuntu:~# In Synology, move share folder to another volume is quite easy, can be done via UI interface. In TrueNAS, I could not find such task can be selected.
The workable solution is utilize the zfs command to duplicate in SSH environment, then export old pool and import new one.
First make a snapshot poolX/dataset@initial, then use following command duplicate zfs dataset snapshot to new zpool.
zfs send poolX/dataset@initial | zfs recv -F poolY/datasetThen make another snapshot poolX/dataset@incremental, then use following command update zfs dataset snapshot to new zpool.
zfs send -i initial poolX/dataset@incremental | zfs recv poolY/datasetTo make the new dataset usable, rollback snapshot needs to be performed for new dataset.
Change shared point to use new pool.
This is only required if client used server filesystem structure, such as NFS.
Migrate to smaller disk
*Note: pv (Pipe Viewer) command is not installed in TrueNAS by default.