Ask Question. Asked 6 years, 11 months ago. Active 2 years, 10 months ago. Viewed 4k times. I understand that the VMWare KB frowns upon long running snapshots mainly due to two things In my opinion Taking tons of snapshots can fill up the data store. Their warnings seem to make logical sense. I want to make my tree the following: Base Snap1 Snap 2 You are here Snap 1 and 2 will be taken immediately after installing and provisioning the base system.
I can not see how this could have any implications for the following reasons: Since I simply installed a base image and took my deltas immediately after there is no way I could possibly fill up the data store. Any thoughts? ESXI 5. I do not have a vCenter license so templating and cloning is off the table.
Before Snapshotting: After Snapshotting:. Improve this question. Not surely - as time goes, the snapshots will diverge more and more. Finally, they will be essentially different copies. After you don't spare much disk by snapshotting them, convert the snapshot to a completely separate volume.
Normally, I use dd from a third VM, but mostly I am nearly crucified here for such heretic opinions, as this.
PeterHorvath - That's the stuff I love to hear. Smart, hacky, effective, bare-bones solutions. If you don't mind could you give me a write up on what you do in pastebin or something? If I needed to do that more often, I did it with a script.
But it is not the case, and in most cases I don't use even snapshpts, becaise they are slow. Add a comment. Active Oldest Votes. Improve this answer.
Interesting, I'll look into that and se how it works. Also the templating and cloning seems no different than taking an OVA and redeploying it.
Deleting the snapshots seem a lot quicker and I can't logically see how there would be performance implications even if it's not the "Official VMWare approved method". To respond to your edit, could you point me to an article or explain what the performance implications would be? I can't see how there would be any assuming I use them how I describe. I guess I'm trying to understand why you're insisting on designing around a feature that's meant to be used for short-term access.
Sometimes, buying the right solution makes sense. Show 2 more comments. I'm almost sure snapshots use a "which block is in which file" table. So reading one single block will only result in one block read from the appropriate file. Of course, reading several blocks may result in accessing several files, which means a penalty for moving disk heads if you're not running from an SSD, but the total number of disk block accesses shouldn't change.
The way I understand it, snapshots only store changes from the original disk. If you store file A, then take a snapshot, then change file A again, only the changes to that file are written to the snapshot. Thus, you need to read both the original VMDK and the snapshot to get the entire file.
Otherwise, each snapshot would simply be a full copy of the original disk, which they aren't. ESXi first checks the existing snapshots for the blocks needed until it ends up at the correct snapshot or the base disk. The key thing is not taking the snapshot itself, but what you do with your snapshot when you are done with it. If you see issues in your environment from VMware snapshots, 9 times out of 10 they will be because a snapshot was left open in perpetuity. After you take the VMware snapshot, all other changes that are made to a VM are stored to a delta file.
This delta file of course grows and grows as the snapshot is left open, and changes are made. Every write from your snapshot forward ends up in the delta file.
Think of a VM that makes lots of transactions without intervention, like a database. All of these changes are written to this delta file. This delta file, more importantly the size of this delta file is very important when it comes to VMware snapshots. Beyond the delta file, there are additional files created when taking a VMware snapshot. If your change goes great, fantastic! However, you now need to delete that snapshot, or keep your changes.
This is where you will see issues with VMware snapshot performance, not necessarily taking the snapshot or having it open, but when it comes time to delete the snapshot. Once, I had a major storage performance issue in an environment when I was a VMware administrator, and we discovered it because snapshots were literally taking DAYS to delete. The other drawback of VMware snapshots is that they are easy to forget about, which can once again lead to the first drawback.
The most useful script we had in our VMware environment was one that e-mailed us daily with a list of open snapshots in our environment so we could keep track of them before we encountered issues. Some of the things we talked about sound pretty horrible, especially when it comes to the performance when deleting a VMware snapshot. There are many good reasons to use a VMware snapshot, as much as they can be come a problem if they are ignored.
Besides having a clean copy of your VM ready to go if something goes wrong with a patch, upgrade, or test, there is one other major benefit of VMware snapshots. This is a nice way of saying that if something goes terribly wrong with your VM, things will start right up without issue should you need revert to a snapshot.
It requires VMware Tools to be installed in the virtual machine. This stun is performed when the VM has finished current operations. Application consistency is great when it comes to backups. In an ideal world, we want to recover our applications in a consistent state, especially when they are applications like databases or things that are highly transactional.
However, Jest's approach of taking snapshots of the underlying code representation takes away this benefit. What I can say is that for mobile, it's not a good solution. The idea of automated software testing is based on defining behaviour and verifying it.
And here's the biggest problem with Jest's snapshot approach - there's no place where you can define what you expect. In behaviour driven tests you'd explain what the component is supposed to do and then verify if it actually does that. A snapshot just tells you what the component looked like before and what it looks like now.
The decision whether you've fixed a bug, or introduced one, is entirely on you. That's in my opinion the biggest problem with this approach: there's no context that tells us why something changed.
In practise, on bigger PRs, you might be confonted with a big list of snapshot changed and a question from Jest: should those snapshots be updated? When you just want to finish your PR, there's a strong temptation to answer: "sure, why not". However, if you wanted to check them, there's no context there to guide you. You need to put on your detective hat and figure out for each of them what changed, why and whether that's a good thing.
It's a common argument to hear that the main advantage of this type of testing is that it's much easier to test this way. That's absolutely true, they're fairly easy to create. However, that cryteria is only relevant if you're comparing two approaches with similar outcomes. Of course it takes more time to read through your component, decide what its behaviour should be, define those rules and write down a test that verifies them. But there's also infinitely more value in it.
The only benefit I can see in creating tons of snapshot tests over the app is for teams that have an artificial KPI on code coverage. However, the problem here is that code coverage is just not a useful metric of a test suite.
Imagine a big project when a new developer joins.
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