Snapshots are the backups for DartFS. The standard policy has been to keep the 6 most recent monthly snapshots. By Friday December 17, 2021 we will have reduced that to keeping the 3 most recent monthlies. What this means to you, a DartFS user, is that when you accidentally delete DartFS data, you will only have 3 months to recover it instead of 6.
There is nothing you need to do and we do not believe this change will have much impact since the overwhelming majority of requests we get for data restoration occur within a week of the mistake.
Frequently Asked Questions
If you believe there will be little impact to users, why did you email everyone who owns a DartFS lab volume?
- Because, even if you didn't realize it, you can restore data from snapshots by yourself (see related article). We can't know if or when that happens, so we also don't know if some people make a habit of restoring data older than 3 months. In other words, some of you might care and we needed a way to tell you.
Why the rush?
- We are running out of space in DartFS. We have already ordered the next generation of DartFS hardware, but it is not likely to arrive before March 2022. Deleting the older snapshots is the only tool we have to recover enough space to bridge the gap to March.
What if a bunch of us get together and delete data we don't need any more; would that help?
- Not quickly enough. Because of the snapshots, we wouldn't actually recover any space for 6 months. Until then, the data is still stored in a snapshot somewhere and is consuming the same amount of space.
Will you go back to keeping 6 monthly snapshots when the new hardware arrives?
- No, this is a permanent change. Best practice for the Isilon storage platform is to keep 3 (or fewer) monthly snapshots. See the previous question for one reason why. The hardware refresh was always going to be our opportunity to learn from deployment decisions we made 5+ years ago and make some corrections. Reducing the snapshot retention policy is just one of several such changes we will be making.
What is Isilon?
- Isilon is the storage platform that underlies DartFS.
Will DartFS cost less because of this change?
- We don't know yet. Before the new hardware arrives, we will recalculate how much DartFS costs to deliver. Fewer snapshots will drive the price down, but at the same time we have been undercharging for snapshots over the last 5+ years based on a too-low estimate of how much space they consume. The cost of the new hardware and associated maintenance will also factor into a new net price per TB. We will be in touch when we have those numbers, but we do not expect a dramatic change in price.
What if I need backups for longer than 3 months (or 6 months or 12 months...)?
- The two biggest risks to most digital data are user error and hardware failure. Isilon snapshots are great for protecting against user errors which are usually discovered quickly. The Isilon platform also inherently provides excellent protection against hardware failure because both physical hard drives and nodes have built-in redundancy against multiple failures. But, if you have other needs then we would love to discuss alternative solutions with you.
What if I have another question?
- As always, email us at research.computing@dartmouth.edu