Don’t try it at home – NetApp SnapMirror network-free Seeding

Well, this is rather common. Network-free seeding is being performed through using a tape device.
What happens if you do not have a tape device? We have the poor-man’s huge TB disks (SATA for the people) connected to simple PC systems, but no tape…
We perform network-free seeding into disk.

There is a utility called ‘lrep’ which is nice and effective. It forces the use of Qtree-based snapmirror (QSM), which has its own limitations. I advise you’ll read NetApp’s “SnapMirror Async Overview and Best Practices Guide” with id TR3446 for further details.

Limitations:

  • You have to have enough space on the source NetApp device to contain twice the volume you require to replicate
  • You can copy the output replica to an external Windows/Linux/Other system, of a movable type (could be a desktop), with large disks using CIFS or NFS.
  • HIgh CPU usage is guaranteed, as well as high disk usage.
  • You are aware to the fact that this is dangerous, and they will probably won’t like you just a little bit for doing this.

Concept:

Using the command ‘snapmirror store‘ you are able to store initial replica into a tape device for later seeding. The options (/man/Internet) describe how you should use your tape device. You don’t have one, or you don’t have one on each site.

Operation:

  • Create a volume or verify you have enough free space on some existing volume on the source NetApp device.
  • You will require the exact amount of used space on the source volume, give or give a little.
  • I recommend you’ll disable snapshots on the target volume for the duration of this operation, to save space.

Let’s assume that the source volume name is ‘vol2’, and that we have enough free space on /vol/vol1/free_space.

You need to perform the following:

Dangerous – change your privilege level:

priv set diag

Perform the initial SnapMirror

snapmirror store vol2 /vol/vol1/free_space/vol2

Remember – you have to be in ‘diag’ mode for it to work.

Reduce your privileges to normal:

priv set

Track the status through

snapmirror status

When the operation has completed, connect from your external Windows/Linux/Other machine to /vol/vol1/free_space and copy out the file ‘vol2’ which will probably be huge.

Transfer the Windows/Linux/Other system (or only its disk) to the alternate location, create a volume or verify you have enough free space on an existing volume to contain the entire file, and copy it to that location. I will assume it’s the same as on the source NetApp device – /vol/vol1/free_space/

Change your privileges level:

´╗┐´╗┐priv set diag

Create the target volume, and set it to be restricted (the values here are just an example):

vol create vol2 aggr0 100g

vol restrict vol2

Perform a ‘snapmirror retrieve’ operation:

snapmirror retrieve vol2 /vol/vol1/free_space/vol2

Reduce your privileges to normal:

priv set

You can track the status through

snapmirror status

Following that, perform an update with the source NetApp real path (filer1:/vol/vol2) and you’re fine.

Remember – be very very careful when running under ‘diag’ privileges.

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