Sync Isn't What You Think - Graphic by Angela Jeske

Sync Isn't What You Think

The sky’s the limit when you sync data, because syncing makes it easy for you to work with your files from any place. Since syncing is undoubtedly awesome in general, it might seem like a helpful tool for when you’re migrating your company data from one storage to another. But in the context of a large data migration, some kinds of syncing are unnecessary and could even harm rather than help.

In this article, we’re going to explain how syncing can be your enemy during a data migration. But before we get to that, let’s do a quick refresher on what sync is and explain how a Mover migration works so well with minimal syncing.

What is syncing?

When you have a file that lives in two or more places and you want it to be the same everywhere at all times, you need to sync it. This happens with the help of a sync engine. When you change something in that file, a sync engine will replicate the change in all the places where the file lives.

Here’s an everyday example: imagine that your family keeps a grocery list online. When you add bananas to the list from your laptop at home, the new item gets synced. Your partner, who’s just arrived at the grocery store, checks the list from their phone, sees your new request, and gets you those scrumptious bananas.

How syncing works in a Mover data migration

During a migration, one-way syncing from your old place to the new one is fine, and that’s what we do. Here’s an example of how it works:

Cool Company has planned to migrate 100 TB over two weeks. Mover starts migrating the data on a Monday. At the beginning of the migration in our first pass, we copy all 100 TB of Cool Company’s data in three days. This is the big pass that takes the most time during the migration.

On Thursday, we run a delta pass, which means we look through Cool Company’s data to see if anything changed. We see that 100 GB has changed, so we re-migrate, or do a one-way sync, of that 100 GB from the old home to the new.

During the second week of the migration, we true up the data in the new home on a regular basis by running more delta passes. And the delta passes are quick, because we’re not re-migrating all the data. We’re only re-migrating (one-way syncing) the data that’s changed.

The time comes for Cool Company to cut over and leave the old home behind. So on Friday night of the second week, we start running our final delta pass. The pass finishes over the weekend, and the migration is complete. On Monday morning, the staff of Cool Company log into their new cloud home and find all their files completely moved over, up to date, and ready to use.

This is how a migration works with Mover every time, more or less. Our philosophy is that you should move your data as quickly as possible and behind the scenes. Get your migration done and cut over to your new cloud with no dilly-dallying and no syncing except for one-way, from the old home to the new.

So what’s wrong with syncing during a migration?

It seems like syncing makes sure your files stay up to date during a migration, right? Yes. For sure! So what’s the problem? The problem is when you get into two-way sync, particularly going from your new home back to the old one. Here’s what could go wrong when you get into this sort of syncing:

Your data is more likely to get out of sync

When you throw a syncing party during your migration, you increase the likelihood that your data will get out of sync between the two storages.

For example, if you’re giving users access to both places, User #1 could overwrite File A in the old spot while User #2 overwrites it in the new one. File A will conflict with itself, and you’ll have to create a resolution path that picks which version to use. You could potentially lose important changes to the file.

More technical problems and support issues

As data gets out of sync, you will have more technical problems and need support from more places: your old storage provider, for example, plus your new one, and probably your own company’s help desk.

And the problems will be harder to solve, because no cloud storage provider in the world wants to help you sync their product to a competitor.

To top it off, all the cloud storage providers have their own sync products. They don’t sync to their competitors, but they do sync within their cloud ecosystem. So it’s extra confusing to do additional syncing during a migration on top of what’s already going on. In theory, you could have three syncs happening: one by each cloud storage provider and also one between the two. This multi-layered syncing also increases the potential for technical problems.

If users don’t want to move, syncing makes it easier for them to push back

In a syncing party, you’re keeping the old home updated, and users are able to access their files as they always have. Sometimes a business unit might say, “We really like our old place. We’re not gonna move to the new one. Make us.” Syncing makes it easier for users to push back and not adopt your new cloud storage provider.

Syncing enables your users to drag their heels on the migration

If your users are still able to work from the old place because all the company data’s being synced back there, they’ll just stick to status quo and take a lackadaisical approach to the migration. Their rationale will be, “We don’t have to hurry up about this, because we’re syncing all the data.”

Ultimately, syncing reduces your users’ incentive to switch. If they don’t have to, they won’t.

Syncing can prolong your migration and cost you time and money

In addition to users potentially pushing back on the migration and dragging their heels on getting it done, two-way syncing will mean moving more data back and forth. All these factors could prolong your migration, and the consequences are lost time and money. You’ll lose time as you grapple with more technical problems and negotiate with users. And you’ll lose money because of paying to use both storage products longer as your migration drags out.

Keep syncing in its proper role, and you’ll be fine

One-way sync has an important role in a large-scale data migration. If we didn’t do our delta passes in a migration, for example, regularly syncing just the data that’s changed, we might end up moving the entire set of data all over again. And that would be expensive and time-consuming.

But any form of syncing beyond this is bad news. So when you’re embarking on a data migration, remember the role sync should play: from old to new and one-way only.

This is probably more than you ever wanted to know about syncing, but if you’d like to delve deeper into this topic or any other aspect of how to execute a top-notch data migration, Mover is here to help! You can reach us at support@mover.io.

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