FreeBSD Manual Pages

home | help

SIMPLESNAP(8) SIMPLESNAP(8)

NAME
simplesnap - Simple and powerful way to send ZFS snapshots across a
network

SYNOPSIS
simplesnap [ --sshcmd COMMAND ] [ --wrapcmd COMMAND ] [ --receivecmd
COMMAND ] [ --local ] [ --noreap ] [ --backupdataset DATASET
[ --datasetdest DEST ] ] --store STORE --setname NAME --host HOST

simplesnap --check TIMEFRAME --store STORE --setname NAME [ --host HOST
]

simplesnap --reaponly --store STORE --setname NAME [ --host HOST ]

DESCRIPTION
simplesnap is a simple way to send ZFS snapshots across a network. Al-
though it can serve many purposes, its primary goal is to manage back-
ups from one ZFS filesystem to a backup filesystem also running ZFS,
using incremental backups to minimize network traffic and disk usage.

simplesnap is FLEXIBLE; it is designed to perfectly compliment snap-
shotting tools, permitting rotating backups with arbitrary retention
periods. It lets multiple machines back up a single target, lets one
machine back up multiple targets, and keeps it all straight.

simplesnap is EASY; there is no configuration file needed. One ZFS
property is available to exclude datasets/filesystems. ZFS datasets
are automatically discovered on machines being backed up.

simplesnap is designed to maximize SAFETY; it is robust in the face of
interrupted transfers, and needs little help to keep running.

simplesnap is designed to maximize SECURITY; unlike many similar tools,
it does not require full root access to the machines being backed up.
It runs only a small wrapper as root, and the wrapper has only three
commands it implements.

FEATURE LIST
Besides the above, simplesnap:

• Does one thing and does it well. It is designed to be used with a
snapshot auto-rotator on both ends (such as zfSnap). simplesnap will
transfer snapshots made by other tools, but will not destroy them on
either end.

• Requires ssh public key authorization to the host being backed up,
but does not require permission to run arbitrary commands. It has a
wrapper to run on the backup host, written in bash, which accepts
only three operations and performs them simply. It is suitable for a
locked-down authorized_keys file.

• Creates minimal snapshots for its own internal purposes, generally
leaving no more than 1 or 2 per dataset, and reaps them automatically
without touching others.

• Optionally supports ZFS bookmarks, preventing backup-related snap-
shots from consuming space on the system being backed up.

• Is a small program, easily audited. In fact, most of the code is de-
voted to sanity-checking, security, and error checking.

• Automatically discovers what datasets to back up from the remote.
Uses a user-defined zfs property to exclude filesystems that should
not be backed up.

• Logs copiously to syslog on all hosts involved in backups.

• Intelligently supports a single machine being backed up by multiple
backup hosts, or onto multiple sets of backup media (when, for in-
stance, backup media is cycled into offsite storage)

METHOD OF OPERATION
simplesnap's operation is very simple.

The simplesnap program runs on the machine that stores the backups --
we'll call it the backuphost. There is a restricted remote command
wrapper called simplesnapwrap that runs on the machine being backed up
-- we'll call it the activehost. simplesnapwrap is never invoked di-
rectly by the end-user; it is always called remotely by simplesnap.

With simplesnap, the backuphost always connects to the activehost --
never the other way round.

simplesnap runs in the backuphost, and first connects to the sim-
plesnapwrap on the activehost and asks it for a list of the ZFS
datasets ("listfs" operation). simplesnapwrap responds with a list of
all ZFS datasets that were not flagged for exclusion.

Next, simplesnap connects back to simplesnapwrap once for each dataset
to be backed up -- the "sendback" operation. simplesnap passes along
to it only two things: the setname and the dataset (filesystem) name.

simplesnapwrap looks to see if there is an existing simplesnap snapshot
corresponding to that SETNAME. If not, it creates one and sends it as
a full, non-incremental backup. That completes the job for that
dataset.

If there is an existing snapshot for that SETNAME, simplesnapwrap cre-
ates a new one, constructing the snapshot name containing a timestamp
and the SETNAME, then sends an incremental, using the oldest snapshot
from that setname as the basis for zfs send -I.

After the backuphost has observed zfs receive exiting without error, it
contacts simplesnapwrap once more and requests the "reap" operation.
This cleans up the old snapshots for the given SETNAME, leaving only
the most recent. This is a separate operation in simplesnapwrap ensur-
ing that even if the transmission is interrupted, still it will be OK
in the end.

The idea is that some system like zfSnap will be used on both ends to
make periodic snapshots and clean them up. One can use careful prefix
names with zfSnap to use different prefixes on each activehost, and
then implement custom cleanup rules with -F on the holderhost.

QUICK START
This section will describe how a first-time simplesnap user can get up
and running quickly. It assumes you already have simplesnap installed
and working on your system. If not, please follow the instructions in
the INSTALL.txt file in the source distribution.

As above, I will refer to the machine storing the backups as the "back-
uphost" and the machine being backed up as the "activehost".

First, on the backuphost, as root, generate an ssh keypair that will be
used exclusively for simplesnap.

ssh-keygen -t rsa -f ~/.ssh/id_rsa_simplesnap

When prompted for a passphrase, leave it empty.

Now, on the activehost, edit or create a file called ~/.ssh/autho-
rized_keys. Initialize it with the content of ~/.ssh/id_rsa_sim-
plesnap.pub from the backuphost. (Or, add to the end, if you already
have lines in the file.) Then, at the beginning of that one very long
line, add text like this:

command="/usr/sbin/simplesnapwrap",from="1.2.3.4",
no-port-forwarding,no-X11-forwarding,no-pty

(I broke that line into two for readability, but this must all be on a
single line in your file.)

The 1.2.3.4 is the IP address that connections from the backuphost will
appear to come from. It may be omitted if the IP is not static, but it
affords a little extra security. The line will wind up looking like:

command="/usr/sbin/simplesnapwrap",from="1.2.3.4",
no-port-forwarding,no-X11-forwarding,no-pty ssh-rsa AAAA....

(Again, this should all be on one huge line.)

If there are any ZFS datasets you do not want to be backed up, set
org.complete.simplesnap:exclude property on the activehost to on. For
instance:

zfs set org.complete.simplesnap:exclude=on tank/junkdata

Now, back on the backuphost, you should be able to run:

ssh -i ~/.ssh/id_rsa_simplesnap activehost

say yes when asked if you want to add the key to the known_hosts file.
At this point, you should see output containing:

"simplesnapwrap: This program is to be run from ssh."

If you see that, then simplesnapwrap was properly invoked remotely.

Now, create a ZFS filesystem to hold your backups. For instance:

zfs create tank/simplesnap

I often recommend compression for simplesnap datasets, so:

zfs set compression=lz4 tank/simplesnap

(If that gives an error, use compression=on instead.)

I also recommend disabling the creation of /dev/zvol entries for
backed-up filesystems, so:

zfs set volmode=none tank/simplesnap

Now, you can run the backup:

simplesnap --host activehost --setname mainset --store tank/simplesnap
--sshcmd "ssh -i /root/.ssh/id_rsa_simplesnap"

You can monitor progress in /var/log/syslog. If all goes well, you
will see filesystems start to be populated under tank/simplesnap/host.

Simple!

Now, go test that you have the data you expected to: look at your STORE
filesystems and make sure they have everything expected. Test repeat-
edly over time that you can restore as you expect from your backups.

ADVANCED: SETNAME USAGE
Most people will always use the same SETNAME. The SETNAME is used to
track and name the snapshots on the remote end. simplesnap tries to
always leave one snapshot on the remote, to serve as the base for a fu-
ture incremental.

In some situations, you may have multiple bases for incrementals. The
two primary examples are two different backup servers backing up the
same machine, or having two sets of backup media and rotating them to
offsite storage. In these situations, you will have to keep different
snapshots on the activehost for the different backups, since they will
be current to different points in time.

ADVANCED: ZFS BOOKMARKS
simplesnap implements a fairly typical ZFS incremental backup strategy.
Newer versions of ZFS support bookmarks. Bookmarks consume no space on
the server, while snapshots keep their space held.

In practice, this is generally not a problem for backups, since snap-
shots are frequently transferred and old ones removed. In some infre-
quent backup situations, it may be a larger issue, and for those situa-
tions, simplesnap supports bookmarks.

Please note, however, that bookmark support in simplesnap is not well-
used or well-tested; please verify proper operation on non-production
data before attempting to use it for anything important.

One caveat with bookmarks is that zfs send -I is not supported with
them; instead, simplesnap has to fall back to zfs send -i. This causes
the intermediate snapshots to not be transferred. You can work around
this by snapshotting on the receiving end.

So, if after all that, you still want to try it, set the org.com-
plete.simplesnap:createbookmarks property to on for any dataset for
which you'd like to use bookmarks.

OPTIONS
All simplesnap options begin with two dashes (`--'). Most take a para-
meter, which is to be separated from the option by a space. The equals
sign is not a valid separator for simplesnap.

The normal simplesnap mode is backing up. An alternative check mode is
available, which requires fewer parameters. This mode is described be-
low.

--backupdataset DATASET
Normally, simplesnap automatically obtains a list of datasets to
back up from the remote, and backs up all of them except those
that define the org.complete.simplesnap:exclude=on property.
With this option, simplesnap does not bother to ask the remote
for a list of datasets, and instead backs up only the one pre-
cise DATASET given. For now, ignored when --check is given, but
that may change in the future. It would be best to not specify
this option with --check for now.

--check TIMEFRAME
Do not back up, but check existing backups. If any datasets'
newest backup is older than TIMEFRAME, print an error and exit
with a nonzero code. Scans all hosts unless a specific host is
given with --host. The parameter is in the format given to GNU
date(1); for instance, --check "30 days ago". Remember to en-
close it in quotes if it contains spaces.

--reaponly
Do not back up, but perform the reap of old simplesnap-generated
snapshots on the local end. Only useful if --noreap is in use
for backups.

--datasetdest DEST
Valid only with --backupdataset, gives a specific destination
for the backup, whith may be outside the STORE. The STORE must
still exist, as it is used for storing lockfiles and such.

--host HOST
Gives the name of the host to back up. This is both passed to
ssh and used to name the backup sets.

In a few situations, one may not wish to use the same name for
both. It is recommend to use the Host and HostName options in
~/.ssh/config to configure aliases in this situation.

--local
Specifies that the host being backed up is local to the machine.
Do not use ssh to contact it, and invoke the wrapper directly.
You would not need to give --sshcmd in this case. For instance:
simplesnap --local --store /bakfs/simplesnap --host server1
--setname bak1

--noreap
Skips the usual reaping of old simplesnap-generated snapshots on
the destination after a successful receive. Useful when the
destination is not actually ZFS, or in conjunction with a later
--reaponly.

This has no impact on the reaping of old simplesnap-generated
snapshots on the host being backed up; that reaping will con-
tinue as usual.

--sshcmd COMMAND
Gives the command to use to connect to the remote host. De-
faults to "ssh". It may be used to select an alternative con-
figuration file or keypair. Remember to quote it per your shell
if it contains spaces. For example: --sshcmd "ssh -i
/root/.id_rsa_simplesnap". This command is ignored when --local
or --check is given.

--receivecmd COMMAND
Gives the command to use to receive a ZFS dataset; defaults to
"/sbin/zfs receive -u -o readonly=on mountpoint". It is
strongly recommended to never access the backed up datasets di-
rectly, but rather to use clones.

This command does not have to actually be zfs; for instance, in
certain situations, it may be valuable to queue the data or save
it off in a file for use on a non-ZFS target. In those cases,
--noreap should also be given.

--setname SETNAME
Gives the backup set name. Can just be a made-up word if multi-
ple sets are not needed; for instance, the hostname of the
backup server. This is used as part of the snapshot name.

--store STORE
Gives the ZFS dataset name where the data will be stored.
Should not begin with a slash. The mountpoint will be obtained
from the ZFS subsystem. Always required.

--wrapcmd COMMAND
Gives the path to simplesnapwrap (which must be on the remote
machine unless --local is given). Not usually relevant, since
the command parameter in ~root/.ssh/authorized_keys gives the
path. Default: "simplesnapwrap"

BACKUP INTERROGATION
Since simplesnap stores backups in standard ZFS datasets, you can use
standard ZFS tools to obtain information about backups. Here are some
examples.

SPACE USED PER HOST
Try something like this:

# zfs list -r -d 1 tank/store
NAME USED AVAIL REFER MOUNTPOINT
tank/store 540G 867G 34K /tank/store
tank/store/host1 473G 867G 32K /tank/store/host1
tank/store/host2 54.9G 867G 32K /tank/store/host2
tank/store/host3 12.2G 867G 31K /tank/store/host3

Here, you can see that the total size of the simplesnap data is 540G -
the USED value from the top level. In this example, host1 was using
the most space -- 473G -- and host3 the least -- 12.2G. There is 867G
available on this zpool for backups.

The -r parameter to zfs list requests a recursive report, but the -d 1
parameter sets a maximum depth of 1 -- so you can see just the top-
level hosts without all their component datasets.

SPACE USED BY A HOST
Let's say that you had the above example, and want to drill down into
more detail. Perhaps, for instance, we continue the above example and
drill down into host2:

# zfs list -r tank/store/host2
NAME USED AVAIL REFER MOUNTPOINT
tank/store/host2 54.9G 867G 32K /tank/...
tank/store/host2/tank 49.8G 867G 32K /tank/...
tank/store/host2/tank/home 7.39G 867G 6.93G /tank/...
tank/store/host2/tank/vm 42.4G 867G 30K /tank/...
tank/store/host2/tank/vm/vm1 32.0G 867G 29.7G -
tank/store/host2/tank/vm/vm2 10.4G 867G 10.4G -
tank/store/host2/rpool 5.12G 867G 32K /tank/...
tank/store/host2/rpool/misc 521M 867G 521M /tank/...
tank/store/host2/rpool/host2-1 4.61G 867G 33K /tank/...
tank/store/host2/rpool/host2-1/ROOT 317M 867G 312M /tank/...
tank/store/host2/rpool/host2-1/usr 3.76G 867G 3.76G /tank/...
tank/store/host2/rpool/host2-1/var 554M 867G 401M /tank/...

I've trimmed the "mountpoint" column here so it doesn't get too wide
for the screen.

You see here the same 54.9G used as in the previous example, but now
you can trace it down. There were two zpools on host2: tank and rpool.
Most of the backup space -- 49.8G of the 54.9G -- is used by tank, and
only 5.12G by rpool. And in tank, 42.4G is used by vm. Tracing it
down, of that 42.4G used by vm, 32G is in vm1 and 10.4G in vm2. Notice
how the values at each level of the tree include their descendents.

So in this example, vm1 and vm2 are zvols corresponding to virtual ma-
chines, and clearly take up a lot of space. Notice how vm1 says it
uses 32.0G but in the refer column, it only refers to 29.7G? That
means that the latest backup for vm2 used 29.7G, but when you add in
the snapshots for that dataset, the total space consumed is 32.0G.

Let's look at an alternative view that will make the size consumed by
snapshots more clear:

# zfs list -o space -r tank/store/host2
NAME AVAIL USED USEDSNAP USEDDS USEDCHILD
.../host2 867G 54.9G 0 32K 54.9G
.../host2/tank 867G 49.8G 0 32K 49.8G
.../host2/tank/home 867G 7.39G 474M 6.93G 0
.../host2/tank/vm 867G 42.4G 50K 30K 42.4G
.../host2/tank/vm/vm1 867G 32.0G 2.35G 29.7G 0
.../host2/tank/vm/vm1 867G 10.4G 49K 10.4G 0
.../host2/rpool 867G 5.12G 0 32K 5.12G
.../host2/rpool/misc 867G 521M 51K 521M 0
.../host2/rpool/host2-1 867G 4.61G 51K 33K 4.61G
.../host2/rpool/host2-1/ROOT 867G 317M 5.44M 312M 0
.../host2/rpool/host2-1/usr 867G 3.76G 208K 3.76G 0
.../host2/rpool/host2-1/var 867G 554M 153M 401M 0

(Again, I've trimmed some irrelevant columns from this output.)

The AVAIL and USED columns are the same as before, but now you have a
breakdown of what makes up the USED column. USEDSNAP is the space used
by the snapshots of that particular dataset. USEDDS is the space used
by that dataset directly -- the same value as was in REFER before. And
USEDCHILD is the space used by descendents of that dataset.

The USEDSNAP column is the easiest way to see the impact your retention
policies have on your backup space consumption.

VIEWING SNAPSHOTS OF A DATASET
Let's take one example from before -- the 153M of snapshots in
host2-1/var, and see what we can find.

# zfs list -t snap -r tank/store/host2/rpool/host2-1/var
NAME USED AVAIL REFER
...
.../var@host2-hourly-2014-02-11_05.17.02--2d 76K - 402M
.../var@host2-hourly-2014-02-11_06.17.01--2d 77K - 402M
.../var@host2-hourly-2014-02-11_07.17.01--2d 18.8M - 402M
.../var@host2-daily-2014-02-11_07.17.25--1w 79K - 402M
.../var@host2-hourly-2014-02-11_08.17.01--2d 156K - 402M
.../var@host2-monthly-2014-02-11_09.01.36--1m 114K - 402M
...

In this output, the REFER column is the amount of data pointed to by
that snapshot -- that is, the size of /var at the moment the snapshot
is made. And the USED column is the amount of space that would be
freed if just that snapshot were deleted.

Note this important point: it is normal for the sum of the values in
the USED column to be less than the space consumed by the snapshots of
the datasets as reported by USEDSNAP in the previous example. The rea-
son is that the USED column is the data unique to that one snapshot.
If, for instance, 100MB of data existed on the system being backed up
for three hours yesterday, each snapshot could very well show less than
100KB used, because that 100MB isn't unique to a particular snapshot.
Until, that is, two of the three snapshots referncing the 100MB data
are destroyed; then the USED value of the last one referencing it will
suddenly jump to 100MB higher because now it references unique data.

One other point -- an indication that the last backup was successfully
transmitted is the presence of a __simplesnap_...__ snapshot at the end
of the list. Do not delete it.

FINDING WHAT CHANGED OVER TIME
The zfs diff command can let you see what changed over time -- either
across a single snapshot, or across many. Let's take a look.

# zfs diff .../var@host2-hourly-2014-02-11_05.17.02--2d \
.../var@host2-hourly-2014-02-11_06.17.01--2d \
| sort -k2 | less
M /tank/store/host2/rpool/host2-1/var/log/Xorg.0.log
M /tank/store/host2/rpool/host2-1/var/log/auth.log
M /tank/store/host2/rpool/host2-1/var/log/daemon.log
...
M /tank/store/host2/rpool/host2-1/var/spool/anacron/cron.daily
M /tank/store/host2/rpool/host2-1/var/spool/anacron/cron.monthly
M /tank/store/host2/rpool/host2-1/var/spool/anacron/cron.weekly
M /tank/store/host2/rpool/host2-1/var/tmp

Here you can see why there was just a few KB of changes in that snap-
shot: mostly just a little bit of logging was happening on the system.
Now let's inspect the larger snapshot:

# zfs diff .../var@host2-hourly-2014-02-11_07.17.01--2d \
.../var@host2-daily-2014-02-11_07.17.25--1w \
| sort -k2 | less
M /tank/store/host2/rpool/host2-1/var/backups
+ /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.0
- /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.0
+ /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.1.gz
R /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.1.gz -> /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.2.gz
R /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.2.gz -> /tank/store/host2/rpool/host2-1/var/backups/dpkg.status.3.gz
...
M /tank/store/host2/rpool/host2-1/var/cache/apt
R /tank/store/host2/rpool/host2-1/var/cache/apt/pkgcache.bin.KdsMLu -> /tank/store/host2/rpool/host2-1/var/cache/apt/pkgcache.bin

Here you can see some file rotation going on, and a temporary file be-
ing renamed to permanent. Normal daily activity on a system, but now
you know what was taking up space.

WARNINGS, CAUTIONS, AND GOOD PRACTICES
IMPORTANCE OF TESTING
Any backup scheme should be tested carefully before being relied upon
to serve its intended purpose. This item is not simplesnap-specific,
but pertains to every backup solution: test that you are backing up the
data you expect to before you need it.

USE OF ZFS RECEIVE AND SECURITY IMPLICATIONS
In order to account for various situations that could lead to diver-
gence of filesystems, including the simple act of mounting them, sim-
plesnap uses zfs receive -u -o readonly=on.

You are strongly encouraged to import your backuphost zpool with -R, or
at least -N, to prevent a malicious mountpoint property on the sending
side from causing unexpected effects on the backuphost. Further, ac-
cessing the backed-up data should always be done via clone.

EXTRANEOUS SNAPSHOT BUILDUP
Since simplesnap sends all snapshots, it is possible that locally-cre-
ated snapshots made outside of your rotation scheme will also be sent
to your backuphost. These may not be automatically reaped there, and
may stick around. An example at the end of the cron.daily.sim-
plesnap.backuphost file included with simplesnap is one way to check
for these. They could automatically be reaped with zfs destroy as
well, but this must be carefully tuned to local requirements, so an ex-
ample of doing that is intentionally not supplied with the distribu-
tion.

INTERNAL SIMPLESNAP SNAPSHOTS
simplesnap creates snapshots beginning with __simplesnap_ followed by
your SETNAME. Do not create, remove, or alter these snapshots in any
way, either on the activehost or the backuphost. Doing so may lead to
unpredictable side-effects.

BUGS
Ordinarily, an interrupted transfer is no problem for simplesnap. How-
ever, the very first transfer of a dataset poses a bit of a problem,
since the simplesnap wrapper can't detect failure in this one special
case. If your first transfer gets interrupted, simply zfs destroy the
__simplesnap_...__ snapshot on the activehost and rerun. NEVER DESTROY
__simplesnap SNAPSHOTS IN ANY OTHER SITUATION!

If, by way of the org.complete.simplesnap:exclude property or the
--backupdataset or --datasetdest parameters, you do not request a par-
ent dataset to be backed up, but do request a descendent dataset to be
backed up, you may get an error on the first backup because the dataset
tree leading to the destination location for that dataset has not yet
been created. simplesnap performs only the narrow actions you request.
Running an appropriate zfs create command will rectify the situation.

Header And Logo

Peripheral Links

Site Navigation

FreeBSD Manual Pages

Header And Logo

Peripheral Links

Search

Site Navigation

FreeBSD Manual Pages