Clara HD Calibre can't send books to device because "insufficient free space"

[einkpaladin]

First off, I apologize if someone already mentioned this. I've spent the last 20-30 minutes scouring these forums and I can't find one that is quite applicable to this situation.

I also am posting this here because I genuinely don't know what sub-forum to put it since I'm not sure if this is a problem with Calibre, with the KoboTouch plugin, or with the Kobo Clara HD itself.

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The Problem: As the title says, Calibre can't send books to my device, a Kobo Clara HD, because it keeps giving the following error message:

There is insufficient free space in main memory

Traceback (most recent call last):
  File "calibre/gui2/device.py", line 111, in run
  File "calibre/gui2/device.py", line 662, in _upload_books
  File "calibre/devices/kobo/driver.py", line 2317, in upload_books
  File "calibre/devices/usbms/driver.py", line 319, in upload_books
  File "calibre/devices/usbms/device.py", line 965, in _sanity_check
  File "calibre/devices/utils.py", line 37, in sanity_check
calibre.devices.errors.FreeSpaceError: There is insufficient free space in main memory

But I know my device has plenty of space left, at 194.2 MiB, both according to my desktop computer and the "Device information" page on the Kobo itself.

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More Details

• Device Model: Kobo Clara HD
• Software Version: 4.38.23171 (6b370fffff, 10/29/24)
• Updated Recently?: Yes.

• Desktop OS: Linux Mint 22.1 Cinnamon
• Calibre Type: APT, according to the official Linux installation instructions listed under "Binary install" (so not the Flatpak version which I read has an issue with temp file capacities or something like that...
• Calibre Version: 8.9 [22 Aug, 2025]

---

I think I didn't forget any information, but if I did, let me know and I'll try my best.

[gbm]

Just how many ebooks do you have on your clara hd? I have 1331 on mine with 5.1GB left.

My suggestion is to delete some ebooks--at least 500 MB--off of you ereader then try to reload your books.

bernie

Originally Posted by einkpaladin

First off, I apologize if someone already mentioned this. I've spent the last 20-30 minutes scouring these forums and I can't find one that is quite applicable to this situation.

I also am posting this here because I genuinely don't know what sub-forum to put it since I'm not sure if this is a problem with Calibre, with the KoboTouch plugin, or with the Kobo Clara HD itself.

---

The Problem: As the title says, Calibre can't send books to my device, a Kobo Clara HD, because it keeps giving the following error message:

There is insufficient free space in main memory

Traceback (most recent call last):
  File "calibre/gui2/device.py", line 111, in run
  File "calibre/gui2/device.py", line 662, in _upload_books
  File "calibre/devices/kobo/driver.py", line 2317, in upload_books
  File "calibre/devices/usbms/driver.py", line 319, in upload_books
  File "calibre/devices/usbms/device.py", line 965, in _sanity_check
  File "calibre/devices/utils.py", line 37, in sanity_check
calibre.devices.errors.FreeSpaceError: There is insufficient free space in main memory

But I know my device has plenty of space left, at 194.2 MiB, both according to my desktop computer and the "Device information" page on the Kobo itself.

---
More Details

• Device Model: Kobo Clara HD
• Software Version: 4.38.23171 (6b370fffff, 10/29/24)
• Updated Recently?: Yes.

• Desktop OS: Linux Mint 22.1 Cinnamon
• Calibre Type: APT, according to the official Linux installation instructions listed under "Binary install" (so not the Flatpak version which I read has an issue with temp file capacities or something like that...
• Calibre Version: 8.9 [22 Aug, 2025]

---

I think I didn't forget any information, but if I did, let me know and I'll try my best.

[einkpaladin]

Originally Posted by gbm

Just how many ebooks do you have on your clara hd? I have 1331 on mine with 5.1GB left.

My suggestion is to delete some ebooks--at least 500 MB--off of you ereader then try to reload your books.

bernie

I have a total of 136 books on my Clara HD, or 6.6 GiB worth.

My device has 194.2 MiB (≈0.2 GiB) remaining.

So I don't think it's because my device has not enough space...

[Terisa de morgan]

Originally Posted by einkpaladin

I have a total of 136 books on my Clara HD, or 6.6 GiB worth.

My device has 194.2 MiB (≈0.2 GiB) remaining.

So I don't think it's because my device has not enough space...

It depends on the size of the books you want to send. If 136 books get 6.6 GiB...

[einkpaladin]

Originally Posted by Terisa de morgan

It depends on the size of the books you want to send. If 136 books get 6.6 GiB...

Fair enough.

Though I have some books that are very high quality. Professional grade, great-quality images, fantastic typefaces, etc. This is why 136 books take up so much space.

My epub copy of Miss Peregrine's Home for Peculiar Children alone is 27.6 MiB.

I also have a number of books that I could not find in epub format (or with decent formatting due to textual/pictoral layouts in the books) which I had to opt for PDF with, which unfortunately jacks up the file sizes in those case. For instance, the Original Illustrated Sherlock Holmes, containing all "37 short stories and a complete novel from The Strand Magazine ... with all 356 original illustrations by Sidney Paget" and facsimile typefacing and text layout ran up to 167.6 MiB due to all the high-resolution images and HQ formatting (and b/c it's PDF not epub).

These reasons are the main ones why a mere 136 books takes up so much space.

[einkpaladin]

Also,

I AM A FUCKING DUMBASS.

Ahem.... *clears throat* Excuse me. I apologize.

Soooooo yeah of COURSE it won't transfer. The next file on the list is one of those large-ass PDF files, and it's 242 MiB while my free space is only 194.2 MiB.

Which leads me to wonder............

HOW THE CRAP DID I NOT REALIZE THIS BEFORE??

Ugh, I feel so silly... I am SO sorry to have wasted everyone's time here...

[Sirtel]

No worries. These things happen to everyone.

[einkpaladin]

Originally Posted by Sirtel

No worries. These things happen to everyone.

Hehe, thank you.

I'll try not to let it happen again.

Have a good evening/morning/night/whateverthehellthisis!

[Sirtel]

It's the middle of the day here (12.50 p.m., to be exact)

Thanks. Good morning/night/whatever to you too!

[Terisa de morgan]

Well, been there, done that (not with ereader but USB or something like that.....)

[fogice]

You can save some space in your epubs with the Polish Books plugin; you can select "subset fonts" (which removes all the characters from your fonts that don't show up in your books) and "losslessly compress images".

[einkpaladin]

Originally Posted by fogice

You can save some space in your epubs with the Polish Books plugin; you can select "subset fonts" (which removes all the characters from your fonts that don't show up in your books) and "losslessly compress images".

That's really cool! Thanks for the recommendation!

Although I have to ask: is the "losslessly compress images" part referring to the cover images or to images displayed within a book?

[Aleron Ives]

I think it means all images. The dialogue doesn't offer much explanation, but it's probably relying on a modern JPEG implementation that can save space without transcoding. There's a tickbox if you want to do a full lossy recompress at a specific quality setting.