Friday, 6 December 2013

A Difference in Clustered ONTAP v 7-Mode in Deleting SnapMirror Snapshots: Part III

Continuing from Part I and Part II

In this post we demonstrate what happens when you use snapshot delete (without the “set diag” level “-ignore-owners true” flag) on a load-sharing SnapMirror relationship’s reference snapshots. It does not delete, which is good news versus 7-Mode, as this prevents a storage admin accidentally deleting a reference snapshot.

Image: Even more rejoicing…
The Example

To demonstrate, we first walkthrough how to set up a load-sharing mirror for a Vserver root volume, then try deleting the reference snapshots, then see what happens when we try to break the LS mirror relationship (you do not break healthy LS mirrors), and finally show what happens when we snapmirror promote.

n::> vol show vs1_root
  (volume show)
Vserver   Volume       Aggregate    State      Type       Size  Available Used%
--------- ------------ ------------ ---------- ---- ---------- ---------- -----
vs1       vs1_root     aggr1_nac1_01
                                    online     RW         20MB    18.88MB    5%

n::> volume create -volume vs1_root_ls -aggr aggr2_nac1_01 -vserver vs1 -size 20MB -type DP
[Job 113] Job succeeded: Successful

n::> snapmirror create -source-path n://vs1/vs1_root -destination-path n://vs1/vs1_root_ls -type LS
[Job 114] Job succeeded: SnapMirror: done

n::> snapmirror initialize-ls-set -source-path n://vs1/vs1_root
[Job 116] Job is queued: snapmirror initialize-ls-set for source n://vs1/vs1_root.

n::> snapmirror show
Source            Destination  Mirror  Relationship
Path        Type  Path         State   Status       Healthy
----------- ---- ------------ ------- ------------- -------
n://vs1/vs1_root
            LS   n://vs1/vs1_root_ls
                              Snapmirrored
                                      Idle          true

n::> snapshot show vs1_root,vs1_root_ls
Vserver  Volume  Snapshot                        State        Size Total% Used%
-------- ------- ------------------------------- -------- -------- ------ -----
vs1      vs1_root
                 snapmirror.5a944ece-3f34-11e3-9b19-123478563412_7_2147484680.2013-12-06_223541
                                                 valid        60KB     0%   33%
         vs1_root_ls
                 snapmirror.5a944ece-3f34-11e3-9b19-123478563412_7_2147484680.2013-12-06_223541
                                                 valid          0B     0%    0%
2 entries were displayed.

n::> snapshot delete vs1_root_ls -snapshot snapmirror.5a944ece-3f34-11e3-9b19-123478563412_7_2147484680.2013-12-06_223541 -vserver vs1
Error: command failed: Volume is read-only.

n::> snapshot delete vs1_root -snapshot snapmirror.5a944ece-3f34-11e3-9b19-123478563412_7_2147484680.2013-12-06_223541 -vserver vs1
Error: command failed: This Snapshot copy is currently used as a reference Snapshot copy by one or more SnapMirror relationships. Deleting the Snapshot copy can cause future SnapMirror operations to fail.

n::> snapmirror break -source-path n://vs1/vs1_root -destination-path n://vs1/vs1_root_ls
Error: command failed: snapmirror break is not allowed for destination n://vs1/vs1_root_ls in a load-sharing relationship.

n::> snapmirror promote -destination-path n://vs1/vs1_root_ls
Warning: Promote will delete the read-write volume n://vs1/vs1_root and replace it with n://vs1/vs1_root_ls.
Do you want to continue? {y|n}: y

n::> vol show vs1_root*
Vserver   Volume       Aggregate    State      Type       Size  Available Used%
--------- ------------ ------------ ---------- ---- ---------- ---------- -----
vs1       vs1_root_ls  aggr2_nac1_01
                                    online     RW         20MB    18.88MB    5%

Volume Modify Type

You might be wondering what happens if you have deleted the SnapMirror relationship, and either have no source or all the SnapMirror reference snapshots have gone (so no chance of resync.)

Are we stuck with a volume of read-only type DP? NO
Is there a volume modify -type switch/option? NO
How do you make a type DP volume read-write (RW) if there is no existing snapmirror relationship and the source has long gone/lost its snapmirror reference snapshots? Easy! “snapmirror break” will make (convert) the type DP volume to RW!

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