Transporte sans bouger (Moving FlexClone volumes without splitting them)

pch-bigsur4.jpg

I’m somewhat of a music buff. I spent most of my teenage years with headphones glued to my ears, and eventually made my way into college radio as a DJ. I was even once able to interview Layzie Bone from Bone Thugs and Harmony!

(I was DJ Sledgehammer)

https://studentmedia.ncsu.edu/web/?q=training/wknc/how-to-be-a-good-dj

I like most every type of music, from hip hop to rock to indie to bluegrass. For a while, I was really into a band from England called Stereolab. In particular, this song:

It’s a song about technology and how humanity becomes disconnected from one another. The title translates to “Transported without Moving” and its themes still resonate today.

But, for this blog, I wanted to apply “transporte san bouger” to an ONTAP feature that allows you to transport data without moving it – volume rehost – and the limitation it currently has on moving FlexClone volumes.

cluster::*> vol rehost -vserver DEMO -volume clone -destination-vserver NFS 

Error: command failed: Cannot rehost volume "clone" on Vserver "DEMO" because the volume is a clone volume.

What is a FlexClone volume?

To answer this question, let’s start with “what is a FlexVol volume”?

A FlexVol is NetApp’s way of presenting a file system to clients in ONTAP software. Each FlexVol volume has its own unique file system ID and can host data via NAS (via NFS and/or SMB) or SAN (via FCP/iSCSI with LUNs). It’s a logical container for data that allows storage administrators to carve out space for their end users without provisioning the entire array to everyone.

FlexVol volumes can host some very important production data, such as code repositories and databases. Sometimes, people need to be able to work with that data without impacting the production data or taking up a bunch of extra storage space. A FlexClone provides an instant copy of a FlexVol volume, based on a snapshot, that only takes up space for inode pointers to data blocks. Thus, you could clone a FlexVol volume that has 10TB of data in less than a second and use up less than 1MB of additional space.

The clone can be read-only or read-write, depending on what you use it for. If it’s a read-write clone, then any data that is written/deleted/overwritten in the clone will use space. But the initial clone? Negligible. Check out the space usage on the aggregate before and after the clone (physical used):

cluster::*> aggr show-space -aggregate-name aggr1_node1

Aggregate : aggr1_node1

Feature Used Used%
-------------------------------- ---------- ------
Volume Footprints 278.4GB 3%
Aggregate Metadata 2.65GB 0%
Snapshot Reserve 0B 0%
Total Used 281.0GB 3%

Total Physical Used 265.6GB 3%


cluster::*> vol clone create -vserver DEMO -flexclone clone -type RW -parent-vserver DEMO -parent-volume flexvol -junction-active true -foreground true -junction-path /clone
[Job 13563] Job succeeded: Successful


cluster::*> vol show -vserver DEMO -volume flexvol,clone -fields used,aggregate
vserver volume    aggregate used
------- ------    ----------- ------
DEMO    clone     aggr1_node1 1.77GB
DEMO    flexvol   aggr1_node1 1.79GB


cluster::*> aggr show-space -aggregate-name aggr1_node1

Aggregate : aggr1_node1

Feature Used Used%
-------------------------------- ---------- ------
Volume Footprints 283.0GB 4%
Aggregate Metadata 2.64GB 0%
Snapshot Reserve 0B 0%
Total Used 285.6GB 4%

Total Physical Used 265.6GB 3%

Some use cases I’ve heard of are:

That’s not nearly all you can do with clones. Leave feedback in the comments with how  you use clones!

So what’s the problem?

A FlexClone, however, for all its usefulness, isn’t super flexible when it comes to moving it around. In addition to volume rehost being unable to move a FlexClone, a non-disruptive volume move of a clone will result in splitting the clone, as well as negating any storage efficiencies you might have!

cluster::*> volume move start -vserver DEMO -volume clone -destination-aggregate aggr1_node2

Warning: Volume will no longer be a clone volume after the move and any associated space efficiency savings will be lost. Do you want to proceed? {y|n}: n

Yuck.

Fortunately, NetApp has some smart people like Jeff Steiner and Florian Feldhaus, who came up with a way to move a clone around without splitting it – thereby retaining the storage efficiencies!

How? With another cool ONTAP feature – SnapMirror.

What’s a SnapMirror?

SnapMirror is a disaster recovery technology that will replicate – at the block level – an exact copy of data to a destination site. That destination could be remote, or it could be on the same cluster. But, it can also be used to move FlexClone volumes around without losing storage efficiencies!

Wait… why would I want to move a FlexClone?

It might not seem like you’d want to move a FlexClone volume, but there are some reasons. For one, you can’t rehost a clone to a new SVM. So, if you were testing in a SVM and wanted to move your volumes to a new SVM and retain the clones, you would be stuck.

Another use case would be moving from ONTAP running in 7-Mode to clustered ONTAP. Using SnapMirror to move data is much faster in many cases than a file-based copy.

Great! How do I do it?

The basic steps are:

  1. Create a SnapMirror of the parent volume (requires cluster/SVM peering, which is all super easy to do in System Manager now)
  2. Ensure the clone volume has a common snapshot for a snapmirror resync operation
  3. Clone the destination volume
  4. Issue a snapmirror resync on the clone volumes (via CLI)

That’s it! Once you’ve done that, you can break the snapmirror, delete the source volume and clone after a final resync for a quick cutover to the new destination.

Here’s where I did it:

Create a SnapMirror of the parent volume

Use a “mirror” relationship type and “MirrorAllSnapshots” as the policy.

clone-mirror1

clone-mirror3

Ensure the clone volume has a common snapshot for a snapmirror resync operation

You can find the snapshot copies under the “Volumes” menu by clicking on the volume for more details and viewing the “Snapshot copies” tab.

clone-mirror-common-snap

Clone the destination volume

Be sure to select the common snapshot.

clone-vol1

Issue a snapmirror resync on the clone volumes (via CLI)

Since we’re kind of “cheating” here by resyncing a relationship that doesn’t actually exist, we have to use the CLI.

sm-resync.png

Once this is done, the relationship will show up in System Manager:

sm-resync-ocsm

Once that transfer completes, I can update the mirror when I’m ready to cutover, quiesce and break the mirror, point clients the new clone and delete the old one from the source SVM. Or, I can keep both around if I like. Pretty nifty, eh?

Any caveats?

There are a couple that immediately come to mind…

  • FlexClone doesn’t currently work with FlexGroup volumes
  • FlexClone and SnapMirror both require licenses

Questions? Comments? Hit me up in the comments!

Advertisements

2 thoughts on “Transporte sans bouger (Moving FlexClone volumes without splitting them)

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s