Fastest way to run a "one-off" migration of an entire Azure blob storage account to Amazon s3

Phynax · September 4, 2024, 8:28pm

What is the problem you are having with rclone?

Hello,

I have been asked to migrate an entire Azure blob storage container to Amazon S3, this will be a one off migration and the files in the Azure storage container will not change at all during the migration.

I have roughly 50 million blobs totalling around 14TB, but no single directory contains more than 1000 files.

Would rclone be a good tool to use for this task or am I overcomplicating things?

If so, are there any flags I should be looking at that could speed the process (the destination bucket will start empty so 'im thinking that there really isn't a need to do any kind of calculation of which files will need transferring)

I really appreciate your help and apologies if this is posted into the wrong place - I'll happily move it to the correct place if someone could point out where that is.

Thanks for your time.

Run the command 'rclone version' and share the full output of the command.

I do not yet have rclone installed, this is an exploratory question about whether or not rclone would be a good choice for my task. (but i would use the most recent version of rclone if so)

Which cloud storage system are you using? (eg Google Drive)

Azure Blob Storage Containers (Premium ZRS)

Amazon S3

The command you were trying to run (eg `rclone copy /tmp remote:tmp`)

Not applicable to this question, Although if someone does have a sample of a command I could run, that would be very helpful.

Please run 'rclone config redacted' and share the full output. If you get command not found, please make sure to update rclone.

Not applicable to this question.

A log from the command that you were trying to run with the `-vv` flag

Not applicable to this question.

asdffdsa · September 4, 2024, 8:37pm

welcome to the forum,

i would rent a cheap vm from aws, in the same region as the bucket.
then run rclone in that vm using something simple.
rclone move azure: aws: --no-traverse --no-check-dest --retries=1

and i am sure @kapitainsky will be some suggestions ;wink

kapitainsky · September 4, 2024, 8:41pm

Have a look at this Github issue:

github.com/rclone/rclone

Excess memory use when syncing millions of files in one directory

opened 08:44AM - 25 Jul 24 UTC

zackees

bug

## Background - Amazon S3 rclone problems I'm trying to backup a datalake wit…h 100 million files at the root. They are mostly small files < 1mb. rclone was simply not designed for this use case and will eat up all available memory and then crash. There was no machine instance that I could throw at it that would fix this issue. Even running locally in a docker instance would eat up all available memory and then crash. All advice in the forums did nothing to help the situation. And a lot of people seem to be running into this. Therefore I wanted to post this here so that anyone searching for this problem can try our solution. ## Solution in a nutshell: PUT YOUR FILES INTO FOLDERS!!!! What's interesting is the behavior: rclone would never start transferring files, it would always sit there saying 0 files transferred, 0 bytes transferred, eat up all available memory before crashing with an OOM. I tried all the suggestions in the forums, reducing the buffering memory, reducing the number of checkers and transfers. Nothing worked. ## Cause & Fix Without looking at the code or doing any profiling, my hypothesis was that rclone scans an all files in a"directory" into RAM before executing on it. This seems true whether not `--fast-scan` is used or not. Obviously, having 100 million files at the root was causing our org a whole bunch of problems anyway and it's been something that I've wanted to fix for a while, so this problem gave me enough reason to go ahead and re-organize our entire datalakes. Since each file is referenced in our database with a datestamp, I was able to write python scripts that would move these files from the root into folders by the service and year-month (for example name.html -> service/2023-04/name.html) This worked extremely well and I was able to now run rclone and have it at least start transferring some files. However, there were still folders with 5+ million files, and eventually ran into the same out-of-memory error. So again, I further re-organized the files in our datalake into service/yrmo/day. And now that seems to have done the trick. rclone now consistently runs under 2GB memory and I've been able to increase the number of transfers and checkers up to 100 each and have 3mb of buffer per transfer. ## Dead ends All the advice about adjust memory buffers and number of transfers is mostly wrong. They will only cut your minimum memory usage by a constant factor, but will do very little to prevent the absolute unbounded memory that rclone uses for extremely large "directories". If you have this same problem, no amount of setting tweaking will work... you MUST re-organize your data into folders or rclone will just run out of memory every single time. If you have too many files at the root, rclone will simply never start transferring anything and just crash. If one of your subdirectories is too big, you'll get a memory pattern that looks like this: ![image](https://github.com/user-attachments/assets/cad7926e-48b7-46f7-be81-543edc896460) ## Recommendations to the Devs of rclone Please serialize your directory scans to disk if you start exceeding a certain threshold of memory or files in the current directory. You can probably just get away with just always doing that since the disk is so much faster than network anyway. I'm currently doing an inventory scan of our datalakes and 50 million files entries is only taking up 12 gb of disk without any fancy compression. I know you are storing a lot more file information, like metadata, so it could easily be double or triple that. But it is simply so much easier and cheaper to allocate disk space to a docker instance than it is to get a machine with much more ram. An additional pain point about an out of memory issue crash is that when the rclone process gets a kill signal, it will **exit 0** making it look like it succeeded. According to this thread https://github.com/rclone/rclone/issues/7966 this is a feature of linux and you must get the exit code from the operating system instead of the return value of the exited rclone process. This is super scary if you are relying on rclone to backup your datalake but in reality, it starts failing because one of your directories has millions of files in it. I know on Digital Ocean it's easy to see that a docker instance has failed, on Render.com however you'll get a "Run Succeeded" and it's not until you look at the run history that you'll see that in fact your instance ran out of memory. I'm not sure about the other hosting providers. Anyway, I'm glad this huge task is finally over with, and we have started syncing up our data for redundancy and backup purposes. So far so good! ![image](https://github.com/user-attachments/assets/5c2b7096-ade2-45d7-993e-4fd0b0f52196)

Looks like with your data structure you are in good position to do it using rclone.

Both source and destination are enterprise class storage remotes so you do not have to worry about artificial throttling etc.

I would simply start with defaults and measure what speed you get. Then increase transfers and checkers if your network connection is not saturated - this should be only bottleneck I think about really.

Phynax · September 4, 2024, 8:56pm

Thanks both!, I'll rent an EC2 instance then and give it a go, would you have any suggestions for what I should start out with for transfers or are the default values generally pretty good starting place?

Once I start running rclone, is it generally safe to stop the process, change the values for transfers and then restart it again?

Sorry if thats a silly question, I'm totally new to rclone.

asdffdsa · September 4, 2024, 9:29pm

i think it is mostly about saturating the internet connection and minimizing api calls.
exactly how to get that, just follow @kapitainsky approach.

yes, can restart.
fwiw, for testing, i would pick individual folders on the source and run rclone just on that, see the result, then tweak as needed.

and then, in the end, consider https://rclone.org/sponsor/