[DRBD-user] Moving TeraBytes to drbd device

Digimer lists at alteeve.ca
Wed Oct 4 02:09:36 CEST 2017

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On 2017-10-03 06:57 PM, José Andrés Matamoros Guevara wrote:
> I have been consulted about moving multiple Terabytes to a new system
> using drbd to ensure high availability. I have been thinking on multiple
> scenarios to move the data as fast as I can and to have a minimal
> maintenance window to change the systems.
> Is there any how-to or recommendation about it? I know it is not exactly
> a drbd consult but I supposed you have been using it for a while and
> have more idea about a best practice. I have thought to have a backup
> program to copy the data and then update it during the maintenance
> window, but been lots of TB, the reading/writing data time is going to
> be the factor to consider.
> Thanks in advance and best regards, Andres.

The best answer is to engage LINBIT for commercial support if you've
been tasked with a sensitive project and a minimal window to do it in.

That said, I'll share what comes to mind;

If you mean "move" as in "copy the data to a new system that already has
DRBD configured and tested", then it is merely a question of hardware.
Make sure you have a sufficiently fast new system to accept the incoming
volume of data within the prescribed time frame. DRBD itself has minimal
overhead, so it is really a question of the speed of the disks and the
replication link.

If you mean to convert an existing filesystem on existing hardware to be
backed by DRBD, then you need to either grow the backing storage by
~32MiB per TiB of existing data, or setup a matching sized storage
device and configure external metadata. With that extra space, you can
setup DRBD and it will see the existing FS and data fine. You'll need a
full resync to the new peer, of course. Also, test/practice outside prod
thoroughly to be certain you have the steps down pat.

There are docs on how to do this openly available on LINBIT's website.
If you get stuck on certain steps, post specific questions and we'll help.

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