When using rsync to backup my /home folder to an external 1TB SSD, I run out of space, how??

Submitted ⁨⁨10⁩ ⁨hours⁩ ago⁩ by ⁨sbeak@sopuli.xyz⁩ to ⁨nostupidquestions@lemmy.world⁩

When running

rsync -Paz /home/sbird “/run/media/sbird/My Passport/sbird”

As told by someone, I run into a ran out of storage error midway. Why is this? My disk usage is about 385 GiB for my home folder, and there is at least 800 GiB of space in the external SSD (which already has stuff like photos and documents). Does rsync make doubly copies of it or something? That would be kind of silly. Or is it some other issue?

Note that the SSD is from a reputable brand (Western Digital) so it is unlikely that it is reporting a fake amount of storage.

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SlurpingPus@lemmy.world ⁨8⁩ ⁨hours⁩ ago
The simplest explanation for the size difference could be if you have a symlink in your home folder pointing outside it. Idk if rsync traverses symlinks and filesystems by default, i.e. goes into linked folders instead of just copying the link, but you might want to check that. Note also that exFAT doesn’t support symlinks, dunno what rsync does in that case.

It would be useful to run ls -R >file.txt in both the source and target directories and diff the files to see if the directory structure changed. (The -l option would report many changes, since exFAT doesn’t support Unix permissions either.)

As others mentioned, if you have hardlinks in the source, they could be copied multiple times to the target, particularly since exFAT, again, doesn’t have hardlinks. But the primary source of hardlinks in normal usage would probably be git, which employs them to compact its structures, and I doubt it that you have >300 GB of git repositories.

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- Wildmimic@anarchist.nexus ⁨7⁩ ⁨hours⁩ ago
  A second possibility is the deduplication feature of BTRFS. If you made copies of files on your SSD, they only take up space there when changing something - thats how i keep 5 differently modded Cyberpunk 2077 installations on my drive while only taking up a fraction of space that would be needed - I wouldn’t be able to copy this drive 1:1 onto a different filesystem.
  
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  - SlurpingPus@lemmy.world ⁨7⁩ ⁨hours⁩ ago
    Ah, I knew the mention of btrfs heebied my jeebies a little, but forgot about the CoW thing.
    
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- bleistift2@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
  
  Idk if rsync traverses symlinks and filesystems by default,
  
  From the man page:
  
  Beginning with rsync 3.0.0, rsync always sends these implied directories as real directories in the file list, even if a path element is really a symlink on the sending side. This prevents some really unexpected behaviors when copying the full path of a file that you didn’t realize had a symlink in its path.
  
  That means, if you’re transferring the file ~/foo/bar/file.txt, where ~/foo/bar/ is a symlink to ~/foo/baz, the baz directory will essentially be duplicated and end up as the real directory /SSD/foo/bar and /SSD/foo/baz.
  
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  - SlurpingPus@lemmy.world ⁨7⁩ ⁨hours⁩ ago
    Yeah, that would do it. If OP has such symlinks, they probably need to add an exception for rsync.
    
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riskable@programming.dev ⁨5⁩ ⁨hours⁩ ago
Simple: Exfat does not support symbolic links. So every file that’s just a symbolic link on your btrfs filesystem is getting copied in full (the link is being resolved) to your Exfat drive.

Solution don’t use Exfat. For backups from btrfs, I recommend using btrfs with compression enabled.

Also don’t forget to rebalance your btrfs partitions regularly to reclaim lost space! Also, delete old snapshots!

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- sbeak@sopuli.xyz ⁨5⁩ ⁨hours⁩ ago
  That makes a lot of sense. I can’t reformat the external SSD though, since it has a bunch of other files and needs to be used by my family (who are mostly Windows users)
  
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confusedpuppy@lemmy.dbzer0.com ⁨8⁩ ⁨hours⁩ ago
There might be a possibility that recursion is happening and a directory is looping into itself and filling up your storage.

I have some suggestions for your command to help make a more consistent experience with rsync.

1: –dry-run (-n) is great for troubleshooting issues. It performs a fake transfer so you can sort issues before moving any data. Remove this option when you are confident about making changes.

2: –verbose --human-readable (-vh) will give you visual feedback so you can see what is happening. Combine this with --dry-run so you get a full picture of what rsync will attempt to do before any changes are made.

3: –compress (-z) might not be suitable for this specific job, as I understand, it’s meant to compress data during a file transfer intended over a network. In your commands current state, it’s just adding extra processing power which might not be useful for a connected device.

4: If you are transferring directories/folders, I found more consistent behaviour from rsync by adding a trailing slash at the end of a path. For example use “/home/username/folder_name/” and not “/home/username/folder_name”. I’ve run into recursion issues by not using a trailing slash.

Don’t use a trailing slash if you are transferring a single file. That distinction helps me to understand what I’m transferring too.

5: –delete will make sure your source folder and destination folder are a 1:1 match. Any files deleted in the source folder will be deleted in the destination folder. If you want to keep any and all added files in your destination folder, this option can be ignored.

–archive (-a) and –partial --progress (-P) are both good and don’t need to be changed or removed.

If you do happen to be running into a recursion issue that’s filling up your storage, you may need to look into using the –exclude option to exclude the problem folder.

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- sbeak@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
  How do I find which folder is causing problems? When using --verbose and --dry-run, it goes way too fast and the terminal can’t see all of the history
  
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  - bleistift2@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
    You can store the output of rsync in a file by using rsync ALL_THE_OPTIONS_YOU_USED > rsync-output.txt. This creates a file called rsync-output.txt in your current directory which you can inspect later.
    
    This, however means that you won’t see the output right away. You can also use rsync ALL_THE_OPTIONS_YOU_USED | tee rsync-output.txt, which will both create the file and display the output on your terminal while it is being produced.
    
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  - confusedpuppy@lemmy.dbzer0.com ⁨7⁩ ⁨hours⁩ ago
    Does your terminal have a scroll back limit? You may need to change that setting if there is a limit.
    
    That will depend on which terminal you are using and it may have a different name so I can’t really help more with this specific issue. You’ll have to search that up based on the terminal you are using.
    
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bleistift2@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
Personally, I have no more tips that those that have already been presented in this comment section. What I would do now to find out what’s going on is the age-old divide-and-conquer debugging technique:

Using rsync or a file manager (yours is Dolphin), only copy a few top-level directories at a time to your external drive. Note the directories you are about to move before each transfer. After each transfer check if the sizes of the directories on your internal drive (roughly) match those on your external drive (They will probably differ a little bit). You can also use your file manager for that.

If all went fine for the first batch, proceed to the next until you find one where the sizes differ significantly. Then delete that offending batch from the external drive. Divide the offending batch into smaller batches (select fewer directories if you tried transferring multiple; or descend into a single directory and copy its subdirectories piecewise like you did before).

In the end you should have a single directory or file which you have identified as problematic. That can then be investigated further.

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- sbeak@sopuli.xyz ⁨5⁩ ⁨hours⁩ ago
  YIKES, I found that .local is around 30GB on my system ssd, over 50GB in the external SSD. Much of that is due to Steam and Kdenlive. I can try uninstalling Steam…
  
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- sbeak@sopuli.xyz ⁨5⁩ ⁨hours⁩ ago
  Something interesting that I found: according to dolphin, many folders have many GB extra (e.g. 52GB vs 66GB for documents folder which is kind of crazy) while filelight records 52GB vs 112GB for documents folder, which if true, is kind of insane. Using du -sh records 53G vs 136G (they’re the same when using --apparent-size, weird. Specifically for Godot directory, it’s 3.8GB vs 41 GB!!!)!!! Files like videos and games seem to be about the same size, while Godot projects with git are much bigger. Weird.
  
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  - bleistift2@sopuli.xyz ⁨5⁩ ⁨hours⁩ ago
    These differences really are insane. Maybe someone more knowledgeable can comment on why different tools differ so wildly in the total size they report.
    
    I have never used BTRFS, so I must resort to forwarding googled results like this one.
    
    Could you try compsize ~? If the Perc column is much lower than 100% or the Disk Usage column is much lower than the Uncompressed column, then you have some BTRFS-specific file-size reduction on your hands, which your external exFAT naturally can’t replicate.
    
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  - bleistift2@sopuli.xyz ⁨4⁩ ⁨hours⁩ ago
    It’s good you found some pathological examples, but I’m at the end of my rope here.
    
    You can use these examples and the other information you gathered so far and ask specifically how these size discrepancies can be explained and maybe mitigated. I suggest more specialized communities for this such as !linux@lemmy.ml, !linux@programming.dev, !linux@lemmy.world, !linux4noobs@programming.dev, !linux4noobs@lemmy.world, !linuxquestions@lemmy.zip.
    
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  - sbeak@sopuli.xyz ⁨5⁩ ⁨hours⁩ ago
    I’m assuming that Filelight count file size differently, and I will be trusting the result from dolphin more
    
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  - sbeak@sopuli.xyz ⁨5⁩ ⁨hours⁩ ago
    using -H with rsync doesn’t seem to do anything unfortunately…
    
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  - sbeak@sopuli.xyz ⁨5⁩ ⁨hours⁩ ago
    With Dolphin Godot directory is 1GB vs 5GB. Why is there a difference between filelight, dolphin, and du -sh? So weird
    
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- sbeak@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
  Oh that’s actually a good idea. Thanks person! I will report back soon
  
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bleistift2@sopuli.xyz ⁨9⁩ ⁨hours⁩ ago
Could it be you have lots of tiny files and/or a rather large-ish block size on your SSD?

You can check the block size with sude blockdev --getbsz /dev/$THE_DEVICE.

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- sbeak@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
  using the command returns 512 for the external SSD and 4096 for the SSD in my laptop. What does that mean?
  
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  - bleistift2@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
    
    What does that mean?
    
    Imagine your hard drive like a giant cupboard of drawers. Each drawer can only have one label, so you must only ever store one “thing” in one drawer, otherwise you wouldn’t be able to label the thing accurately and end up not knowing what went where.
    
    If you have giant drawers (a large block size), but only tiny things (small files) to store, you end up wasting a lot of space in the drawer. It could fit a desktop computer, but you’re only putting in a phone. This problem is called “internal fragmentation” and causes files to take up way more space than it would seem they need.
    
    –––––
    
    However, in your case, the target block size is actually smaller, so this is not the issue you’re facing.
    
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  - SlurpingPus@lemmy.world ⁨7⁩ ⁨hours⁩ ago
    Means a file that’s 512 bytes in size will take 512 bytes on the external disk, but at minimum 4 KB on the internal one. If it were the other way around, that would partially explain the difference in space used.
    
    In any case, I doubt it that the block sizes would make so much difference in typical usage.
    
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olosta@lemmy.world ⁨9⁩ ⁨hours⁩ ago
Maybe you have hard links or sparse files in your source directory. Try with -H for hard links first. You can try with --sparse but I think hard links are more likely.

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- sbeak@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
  Using -H throws an error as symlinks aren’t supported in exFAT it seems.
  
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  - SlurpingPus@lemmy.world ⁨7⁩ ⁨hours⁩ ago
    By the way, do you have lots of torrents downloaded or large virtual machines installed? Both torrent clients and virtual machine managers use ‘sparse files’ to save space until you actually download the whole torrent or write a lot to the VM’s disk. Those files would be copied at full size to exFAT.
    
    If you have folders with such content, you can use e.g. Double Commander to check the actual used size of those folders (with ctrl-L in Doublecmd). Idk which terminal utils might give you those numbers in place, but aforementioned ncdu can calculate them and present as a tree.
    
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- SlurpingPus@lemmy.world ⁨7⁩ ⁨hours⁩ ago
  For a typical user, hard links would be mostly employed by git for its internal structures, and it’s difficult to accumulate over 300 GB of git repos.
  
  Sparse files would actually be more believable, since they’re used by both torrent clients and virtual machines.
  
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bleistift2@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
Let’s back up and check your assumptions: How did you check that the disk usage of your home folder is 385GiB and that there are 780GiB of free disk space on your external drive?

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- sbeak@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
  Using du -sh --apparent-size /home/sbird returns 382G, with external SSD 129G (as expected)
  
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  - Dirtboy@lemmy.world ⁨7⁩ ⁨hours⁩ ago
    Is your external SSD partitioned into multiple drives? Are you saying that your SSD is reported to be 129GB by the OS?
    
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- sbeak@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
  Checking “properties” using Dolphin. Could that be incorrect?
  
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  - Dirtboy@lemmy.world ⁨7⁩ ⁨hours⁩ ago
    Does that include hidden folders?
    
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  - bleistift2@sopuli.xyz ⁨7⁩ ⁨hours⁩ ago
    I’d say you can trust that.
    
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whyNotSquirrel@sh.itjust.works ⁨9⁩ ⁨hours⁩ ago
is it pointing to the good folder? I’m never sure if quotes are enough to escape “space” characters (I avoid those to limit troubles actually)

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- bleistift2@sopuli.xyz ⁨9⁩ ⁨hours⁩ ago
  Spaces are enough to handle spaces. That file path is valid.
  
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