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Operating Systems Solaris Understanding ZFS Snapshots - why will it utilize space ? Post 303013453 by Peasant on Wednesday 21st of February 2018 02:08:33 PM
Old 02-21-2018
In a nutshell yes.
It is confusing a bit from user perspective,zfs used/usedsnap etc.

I would recommend reading about snapshots and COW in general.
Any tech that uses those, basically works on same principle.

Range is from filesystems (zfs,brtfs etc.) to enterprise storage systems with proprietary HW/SW.
Everything works the same way more or less.

Lets say blocks need to be modified due to write request.

Instead of overwriting blocks, zfs will write a change a new blocks, while old blocks will still contain old data, and that data will remain on disk until needed and is considered free.

This is what enables snapshots,clones, rollback etc. which is fundamental design of zfs filesystem/volume manager.

If there is a snapshot (pointers to old blocks at the time snapshot is taken), those will not be considered free but will remain unchanged (read the blog i posted, it is extremely good).
This is what enables snapshots,clones, rollback etc.

ZFS is a great and fairly complex product code wise with a lot of time and effort put into it.

One can only put a hat down to those SUN engineers behind it.
Those guys were ahead of their time.

Also, i must apologize upfront for information given in this post due to minor alcohol intoxication Smilie
This happens you know, when you are in automation business.
As a folks say here
'An idle mind is a devils workshop' Smilie

Regards
Peasant.
This User Gave Thanks to Peasant For This Post:
 

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AMZFS-SNAPSHOT(8)					  System Administration Commands					 AMZFS-SNAPSHOT(8)

NAME
amzfs-snapshot - Amanda script to create zfs snapshot DESCRIPTION
amzfs-snapshot is an Amanda script implementing the Script API. It should not be run by users directly. It create a zfs snapshot of the filesystem where the path specified is mounted. PRE-DLE-* create a snapshot and the POST-DLE-* destroy the snapshot, *-DLE-AMCHECK, *-DLE-ESTIMATE and *-DLE-BACKUP must be set to be executed on the client: execute-on pre-dle-amcheck, post-dle-amcheck, pre-dle-estimate, post-dle-estimate, pre-dle-backup, post-dle-backup execute-where client The PRE_DLE_* script output a DIRECTORY property telling where the directory is located in the snapshot. The application must be able to use the DIRECTORY property, amgtar can do it. The script is run as the amanda user, it must have the priviledge to create and destroy snapshot: zfs allow -ldu AMANDA_USER mount,snapshot,destroy FILESYSTEM Some system doesn't have "zfs allow", but you can give the Amanda backup user the rights to manipulate ZFS filesystems by using the following command: usermod -P "ZFS File System Management,ZFS Storage Management" AMANDA_USER This will require that your run zfs under pfexec, set the PFEXEC property to YES. The format of the DLE must be one of: Desciption Example ---------- ------- Mountpoint /data Arbitrary mounted dir /data/interesting_dir ZFS pool name datapool ZFS filesystem datapool/database ZFS logical volume datapool/dbvol The filesystem must be mounted. PROPERTIES
This section lists the properties that control amzfs-snapshot's functionality. See amanda-scripts(7) for information on the Script API, script configuration. DF-PATH Path to the 'df' binary, search in $PATH by default. ZFS-PATH Path to the 'zfs' binary, search in $PATH by default. PFEXEC-PATH Path to the 'pfexec' binary, search in $PATH by default. PFEXEC If "NO" (the default), pfexec is not used, if set to "YES" then pfexec is used. EXAMPLE
In this example, a dumptype is defined to use amzfs-snapshot script to create a snapshot and use amgtar to backup the snapshot. define script-tool amzfs_snapshot { comment "backup of zfs snapshot" plugin "amzfs-snapshot" execute-on pre-dle-amcheck, post-dle-amcheck, pre-dle-estimate, post-dle-estimate, pre-dle-backup, post-dle-backup execute-where client #property "DF-PATH" "/usr/sbin/df" #property "ZFS-PATH" "/usr/sbin/zfs" #property "PFEXEC-PATH" "/usr/sbin/pfexec" #property "PFEXEC" "NO" } define dumptype user-zfs-amgtar { dt_amgtar script "amzfs_snapshot" } SEE ALSO
amanda(8), amanda.conf(5), amanda-client.conf(5), amanda-scripts(7) The Amanda Wiki: : http://wiki.zmanda.com/ AUTHORS
Jean-Louis Martineau <martineau@zmanda.com> Zmanda, Inc. (http://www.zmanda.com) Dustin J. Mitchell <dustin@zmanda.com> Zmanda, Inc. (http://www.zmanda.com) Amanda 3.3.3 01/10/2013 AMZFS-SNAPSHOT(8)
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