Snapshots are efficient point-in-time copies of volumes that can be either read-write or read-only. Each snapshot is a volume in its own right and can be used freely by applications. They are implemented using a copy-on-write technique, so that they only use space in places where they differ from their parent volume. Snapshots can be created explicitly by
pxctl snap create commands or through a schedule that is set on the volume.
pxctl snapshot commands
Snapshots are managed with the
pxctl snap command.
NAME: pxctl snap - Manage volume snapshots USAGE: pxctl snap command [command options] [arguments...] COMMANDS: create, c Create a volume snapshot list, l List volume snapshots in the cluster delete, d Delete a volume snapshot OPTIONS: --help, -h show help
pxctl snap create to make a new snapshot of a volume. A typical example looks like this:
pxctl snap create --name mysnap --label color=blue,fabric=wool myvol
Volume successfully snapped: 1152602487227170184
The string of digits in the output is the volume ID of the new snapshot. You can use this ID or the name,
mysnap, to refer to the snapshot in subsequent
pxctl commands. The label values allow you to tag the snapshot with descriptive information of your choosing. You can use them to filter the output of the
pxctl snap list command, as described below.
The parent volume,
myvol, must be attached and all nodes that contain volume data must be accessible in order for this command to succeed. If these conditions do not hold, the system will try creating a snapshot 10 minutes later and keep retrying until it succeeds. The resulting snapshot will not have the name specified in your command, but will have a name of the form
Here is the synopsis for
pxctl snap create:
NAME: pxctl snap create - Create a volume snapshot USAGE: pxctl snap create [command options] [arguments...] OPTIONS: --name value user friendly name --label pairs, -l pairs list of comma-separated name=value pairs --readonly true if snapshot is readonly
The argument is the name or ID of the parent volume on which the snapshot is based. By default, the snapshot will be writable, but you can make it read-only with the
--readonly option. If you omit the
--name option, a default name is assigned. Its format is
<parent-ID>.snap-<creation-time>, for example,
Each snapshot is a volume and can be used like any other volume. For instance, you can attach it and can create snapshots of it:
pxctl host attach mysnap
Volume successfully attached at: /dev/pxd/pxd1152602487227170184
pxctl snap create --name mysnap_jr mysnap
Volume successfully snapped: 1312421116276761727
However, snapshots do not appear in the output of
pxctl volume list. To list them, use
pxctl snap list. As with other volumes, you can use
pxctl volume inspect to see more detailed information.
There is an implementation limit of 64 snapshots per volume.
NAME: pxctl snap list - List volume snapshots in the cluster USAGE: pxctl snap list [command options] [arguments...] OPTIONS: --parent value parent volume ID --label pairs, -l pairs Comma separated name=pairs pairs
If you run this command with no options, you get a list of all snapshots, with information about their attributes:
pxctl snap list
ID NAME SIZE HA SHARED STATUS 1152602487227170184 mysnap 1 GiB 1 no up - attached on 10.0.2.15 1312421116276761727 mysnap_jr 1 GiB 1 no up - detached
You can filter the results with the
--label options. For instance,
--parent myvol will show only snapshots whose parent is
mysnap in this example. Giving labels restricts the list to snapshots that have all of the specified labels. For instance,
--label fabric=wool would again show
--label fabric=cotton would produce an empty list.
NAME: pxctl snap delete - Delete a volume snapshot USAGE: pxctl snap delete [arguments...]
The argument is the name or ID of the snapshot that you wish to delete. The snapshot must be detached in order to delete it.
In addition to creating snapshots explicitly with the
pxctl snap create command, you can create them automatically according to a per-volume schedule. There are four scheduling options, which you can combine as desired. A daily snapshot is created every day at a specified time, a weekly snapshot is created on a specified day of the week, and a monthly snapshot is created on a specified day of the month. Finally, you can specify that snapshots should be created at a fixed interval, say every 60 minutes. The example below sets a schedule of daily snapshots at 8:00 a.m. and 6:00 p.m., a weekly snapshot on Friday at 11:30 p.m., and a monthly snapshot on the 1st of the month at 6:00 a.m.
pxctl volume create --daily @08:00 --daily @18:00 --weekly Friday@23:30 --monthly 1@06:00 myvol
Interval-based snapshots are set with the
--snap_interval option. As a special case
--snap_interval 0 removes any current snapshot schedule.
The snapshot schedule can be changed with the
pxctl volume snap-interval-update command. It accepts the same scheduling arguments as the create command:
pxctl volume snap-interval-update --daily @15:00 myvol
If a schedule is set,
pxctl volume inspect will display it:
pxctl volume inspect tester
Volume : 593988376247244600 Name : tester Size : 1.0 GiB Format : ext4 HA : 1 IO Priority : LOW Snapshot : daily @15:00 Shared : no Status : up State : Attached: b9289d88-229b-4c49-b1d1-497a84a37acf Device Path : /dev/pxd/pxd593988376247244600 Reads : 60 Reads MS : 69 Bytes Read : 466944 Writes : 0 Writes MS : 0 Bytes Written : 0 IOs in progress : 0 Bytes used : 33 MiB Replica sets on nodes: Set 0 Node : 10.0.2.15
Scheduled snapshots have names of the form
<freq> denotes the schedule frequency, i.e., daily, weekly, monthly, or periodic. For example,
There is an implementation limit of five scheduled snapshots per volume. When a new scheduled snapshot is created, the oldest existing one will be deleted if necessary to keep the total under five.